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## 97 Package trigtools

Next: Functions and Variables for trigtools, Previous: Package trigtools, Up: Package trigtools [Contents][Index]

# Trigtools Package

Aleksas Dormarkas
aleksasd873@gmail.com
aleksas.domarkas@mif.vu.lt
December 1, 2013

### 97.1 Introduction to trigtools

We use open-source computer algebra system(CAS) maxima 5.31.2. The trigtools package10 contains commands that help you work with trigonometric expessions. List of functions in trigtools package:

- `c2sin`
- `c2cos`
- `c2trig`
- `c2hyp`
- `trigfactor`
- `trigsolve`
- `trigvalue`
- `trigeval`
- `atan_contract`

Categories: Trigonometric functions · Package trigtools ·

Next: References, Previous: Introduction to trigtools, Up: Package trigtools [Contents][Index]

### 97.2 Functions and Variables for trigtools

Next: Convert to Trignometric Functions, Previous: Functions and Variables for trigtools, Up: Functions and Variables for trigtools [Contents][Index]

#### 97.2.1 Convert to sin and cos

Function: c2sin (x)
Function: c2cos (x)

  The function c2sin converts the expression \(a\cos x + b\sin x\) to \(r\sin(x+\phi).\)

  The function c2cos converts the expression \(a\cos x + b\sin x\) to \(r\cos(x-\phi).\)

  `load("trigtools")` loads these functions.

  Examples:

      (%i1) load("trigtools")$
      (%i2) c2sin(3*sin(x)+4*cos(x));
                                                  4
      (%o2)                        5 sin(x + atan(-))
                                                  3
      (%i3) trigexpand(%),expand;
      (%o3)                        3 sin(x) + 4 cos(x)

      (%i4) c2cos(3*sin(x)-4*cos(x));
                                                   3
      (%o4)                       - 5 cos(x + atan(-))
                                                   4

      (%i5) trigexpand(%),expand;
      (%o5)                        3 sin(x) - 4 cos(x)

      (%i6) c2sin(sin(x)+cos(x));
                                                  %pi
      (%o6)                       sqrt(2) sin(x + ---)
                                                   4

      (%i7) trigexpand(%),expand;
      (%o7)                          sin(x) + cos(x)
      (%i8) c2cos(sin(x)+cos(x));
                                                  %pi
      (%o8)                       sqrt(2) cos(x - ---)
                                                   4

      (%i9) trigexpand(%),expand;
      (%o9)                          sin(x) + cos(x)

  Example. Solve trigonometric equation

      (%i10) eq:3*sin(x)+4*cos(x)=2;
      (%o10)                      3 sin(x) + 4 cos(x) = 2

      (%i11) plot2d([3*sin(x)+4*cos(x),2],[x,-%pi,%pi]);

      (%i12) eq1:c2sin(lhs(eq))=2;
                                                 4
      (%o35)                      5 sin(x + atan(-)) = 2
                                                 3
      (%i13) solvetrigwarn:false$
      (%i14) solve(eq1)[1]$ x1:rhs(%);
                                          2         4
      (%o15)                         asin(-) - atan(-)
                                          5         3
      (%i16) float(%), numer;
      (%o39)                       - 0.5157783719341241
      (%i17) eq2:c2cos(lhs(eq))=2;
                                                 3
      (%o17)                      5 cos(x - atan(-)) = 2
      (%i18) solve(eq2,x)[1]$ x2:rhs(%);
                                          3         2
      (%o19)                         atan(-) + acos(-)
                                          4         5
      (%i20) float(%), numer;
      (%o20)                         1.802780589520693

      (%i21) sol:[x1,x2];
                                2         4        3         2
      (%o44)              [asin(-) - atan(-), atan(-) + acos(-)]
                                5         3        4         5

  Answ.: \(x = x_1 + 2\pi k,\) \(x_1 = \sin^{-1}{2\over 5} - \tan^{-1}{4\over 3},\) or \(x_1 = \tan^{-1}{3\over 4} + \cos^{-1}{2\over 5},\) for k any integer.

  Categories: Trigonometric functions · Hyperbolic functions · Package trigtools ·

Next: Convert to Hyperbolic Functions, Previous: Convert to sin and cos, Up: Functions and Variables for trigtools [Contents][Index]

#### 97.2.2 Convert to Trignometric Functions

Function: c2trig (x)

  The function c2trig (convert to trigonometric) reduce expression with hyperbolic functions sinh, cosh, tanh, coth to trigonometric expression with sin, cos, tan, cot.

  `load("trigtools")` loads these functions.

  Examples:

  1.     (%i1) load(trigtools)$
         (%i2) sinh(x)=c2trig(sinh(x));
         cosh(x)=c2trig(cosh(x));
         tanh(x)=c2trig(tanh(x));
         coth(x)=c2trig(coth(x));
         (%o2)                     sinh(x) = - %i sin(%i x)
         (%o3)                        cosh(x) = cos(%i x)
         (%o4)                     tanh(x) = - %i tan(%i x)
         (%o5)                      coth(x) = %i cot(%i x)

  2. see http://www.math.utexas.edu/pipermail/maxima/2013/034585.html

         (%i6) cos(p+q*%i);
         (%o6)                           cos(%i q + p)
         (%i7) trigexpand(%);
         (%o7)                cos(p) cosh(q) - %i sin(p) sinh(q)
         (%i8) c2trig(%);
         (%o8)                           cos(%i q + p)

  3.     (%i9) sin(a+b*%i);
         (%o9)                           sin(%i b + a)
         (%i10) trigexpand(%);
         (%o10)                %i cos(a) sinh(b) + sin(a) cosh(b)
         (%i11) c2trig(%);
         (%o11)                           sin(%i b + a)

  4.     (%i12) cos(a*%i+b*%i);
         (%o12)                         cos(%i b + %i a)
         (%i13) trigexpand(%);
         (%o13)                 sinh(a) sinh(b) + cosh(a) cosh(b)
         (%i14) c2trig(%);
         (%o14)                         cos(%i b + %i a)

  5.     (%i15) tan(a+%i*b);
         (%o15)                           tan(%i b + a)

         (%i16) trigexpand(%);
                                       %i tanh(b) + tan(a)
         (%o16)                       ---------------------
                                      1 - %i tan(a) tanh(b)

         (%i17) c2trig(%);
         (%o217)                           tan(%i b + a)

  6.     (%i18) cot(x+%i*y);
         (%o18)                           cot(%i y + x)
         (%i19) trigexpand(%);
                                    (- %i cot(x) coth(y)) - 1
         (%o19)                     -------------------------
                                       cot(x) - %i coth(y)
         (%i20) c2trig(%);
         (%o20)                           cot(%i y + x)

  Categories: Trigonometric functions · Package trigtools ·

Next: Factor Sums of sin and cos Functions, Previous: Convert to Trignometric Functions, Up: Functions and Variables for trigtools [Contents][Index]

#### 97.2.3 Convert to Hyperbolic Functions

Function: c2hyp (x)

  The function c2hyp (convert to hyperbolic) convert expression with exp function to expression with hyperbolic functions sinh, cosh.

  `load("trigtools")` loads this function.

  Examples:

      (%i6) c2hyp(exp(x));
      (%o6)                         sinh(x) + cosh(x)
      (%i7) c2hyp(exp(x)+exp(x^2)+1);
                             2          2
      (%o7)            sinh(x ) + cosh(x ) + sinh(x) + cosh(x) + 1
      (%i8) c2hyp(exp(x)/(2*exp(y)-3*exp(z)));
                                    sinh(x) + cosh(x)
      (%o8)           ---------------------------------------------
                      2 (sinh(y) + cosh(y)) - 3 (sinh(z) + cosh(z))

  Categories: Trigonometric functions · Hyperbolic functions · Package trigtools ·

Next: Solve Trignometric Equations, Previous: Convert to Hyperbolic Functions, Up: Functions and Variables for trigtools [Contents][Index]

#### 97.2.4 Factor Sums of sin and cos Functions

Function: trigfactor (x)

  The function trigfactor factors expresions of form \(\pm \sin x \pm \cos y.\)

  `load("trigtools")` loads this function.

  Examples:

  1.     (%i2) trigfactor(sin(x)+cos(x));
                                                     %pi
         (%o2)                       sqrt(2) cos(x - ---)
                                                      4
         (%i3) trigrat(%);
         (%o3)                          sin(x) + cos(x)

  2.     (%i4) trigfactor(sin(x)+cos(y));
                                    y   x   %pi      y   x   %pi
         (%o4)                2 cos(- - - + ---) cos(- + - - ---)
                                    2   2    4       2   2    4

         (%i5) trigrat(%);
         (%o5)                          cos(y) + sin(x)

  3.     (%i6) trigfactor(sin(x)-cos(3*y));
                                  3 y   x   %pi      3 y   x   %pi
         (%o6)              2 sin(--- - - + ---) sin(--- + - - ---)
                                   2    2    4        2    2    4
         (%i7) trigrat(%);
         (%o7)                         sin(x) - cos(3 y)

  4.     (%i8) trigfactor(-sin(5*x)-cos(3*y));
                                 3 y   5 x   %pi      3 y   5 x   %pi
         (%o8)           - 2 cos(--- - --- + ---) cos(--- + --- - ---)
                                  2     2     4        2     2     4
         (%i9) trigrat(%);
         (%o9)                      (- cos(3 y)) - sin(5 x)

  5.     (%i10) sin(alpha)+sin(beta)=trigfactor(sin(alpha)+sin(beta));
                                                beta   alpha      beta   alpha
         (%o10)  sin(beta) + sin(alpha) = 2 cos(---- - -----) sin(---- + -----)
                                                 2       2         2       2

         (%i11) trigrat(%);
         (%o78)          sin(beta) + sin(alpha) = sin(beta) + sin(alpha)

  6.     (%i12) sin(alpha)-sin(beta)=trigfactor(sin(alpha)-sin(beta));
                                                 beta   alpha      beta   alpha
         (%o12) sin(alpha) - sin(beta) = - 2 sin(---- - -----) cos(---- + -----)
                                                  2       2         2       2

  7.     (%i13) cos(alpha)+cos(beta)=trigfactor(cos(alpha)+cos(beta));
                                                beta   alpha      beta   alpha
         (%o80)  cos(beta) + cos(alpha) = 2 cos(---- - -----) cos(---- + -----)
                                                 2       2         2       2

  8.     (%i14) cos(alpha)-cos(beta)=trigfactor(cos(alpha)-cos(beta));
                                                beta   alpha      beta   alpha
         (%o14)  cos(alpha) - cos(beta) = 2 sin(---- - -----) sin(---- + -----)
                                                 2       2         2       2

  9.     (%i15) trigfactor(3*sin(x)+7*cos(x));
         (%o15)                        3 sin(x) + 7 cos(x)

         (%i16) c2sin(%);
                                                          7
         (%o16)                     sqrt(58) sin(x + atan(-))
                                                          3

         (%i17) trigexpand(%),expand;
         (%o17)                        3 sin(x) + 7 cos(x)

     10.

         (%i18) trigfactor(sin(2*x));
         (%o18)                             sin(2 x)
         (%i19) trigexpand(%);
         (%o19)                          2 cos(x) sin(x)

  Categories: Trigonometric functions · Package trigtools ·

Next: Evaluation of Trignometric Functions, Previous: Factor Sums of sin and cos Functions, Up: Functions and Variables for trigtools [Contents][Index]

#### 97.2.5 Solve Trignometric Equations

Function: trigsolve (x)

  The function trigsolve find solutions of trigonometric equation from interval \([a,b).\)

  `load("trigtools")` loads this function.

  Examples:

  1.     (%i38) eq:eq:3*sin(x)+4*cos(x)=2;
         (%o38)                      3 sin(x) + 4 cos(x) = 2

         (%i39) plot2d([3*sin(x)+4*cos(x),2],[x,-%pi,%pi]);

         (%o39)
         (%i40) sol:trigsolve(eq,-%pi,%pi);
                           2 sqrt(21)   12              2 sqrt(21)   12
         (%o40)      {atan(---------- - --), %pi - atan(---------- + --)}
                               5        5                   5        5
         (%i41) float(%), numer;
         (%o41)            {- 0.5157783719341241, 1.802780589520693}

     Answ. : \(x = \tan^{-1}\left({2\sqrt{21}\over 5} - {12\over 5}\right) + 2\pi k\) ; \(x = \pi - \tan^{-1}\left({2\sqrt{21}\over 5} + {12\over 5}\right) + 2\pi k,\) k – any integer.

  2.     (%i6) eq:cos(3*x)-sin(x)=sqrt(3)*(cos(x)-sin(3*x));
         (%o6)         cos(3 x) - sin(x) = sqrt(3) (cos(x) - sin(3 x))
         (%i7) plot2d([lhs(eq)-rhs(eq)], [x,0,2*%pi])$

     We have 6 solutions from [0, 2*pi].

         (%i8) plot2d([lhs(eq)-rhs(eq)], [x,0.2,0.5]);

         (%i9) plot2d([lhs(eq)-rhs(eq)], [x,3.3,3.6]);

         (%i10) trigfactor(lhs(eq))=map(trigfactor,rhs(eq));
                            %pi            %pi                      %pi            %pi
         (%o15) - 2 sin(x + ---) sin(2 x - ---) = 2 sqrt(3) sin(x - ---) sin(2 x - ---)
                             4              4                        4              4
         (%i11) factor(lhs(%)-rhs(%));
                          4 x + %pi                4 x - %pi       8 x - %pi
         (%o11)  - 2 (sin(---------) + sqrt(3) sin(---------)) sin(---------)
                              4                        4               4

     Equation is equivalent to

         (%i12) L:factor(rhs(%)-lhs(%));
                         4 x + %pi                4 x - %pi       8 x - %pi
         (%o12)   2 (sin(---------) + sqrt(3) sin(---------)) sin(---------)
                             4                        4               4

         (%i13) eq1:part(L,2)=0;
                              4 x + %pi                4 x - %pi
         (%o13)           sin(---------) + sqrt(3) sin(---------) = 0
                                  4                        4

         (%i14) eq2:part(L,3)=0;
                                          8 x - %pi
         (%o14)                       sin(---------) = 0
                                              4

         (%i15) S1:trigsolve(eq1,0,2*%pi);
                                          %pi  13 %pi
         (%o15)                         {---, ------}
                                          12     12
         (%i16) S2:trigsolve(eq2,0,2*%pi);
                                    %pi  5 %pi  9 %pi  13 %pi
         (%o16)                   {---, -----, -----, ------}
                                     8     8      8      8
         (%i17) S:listify(union(S1,S2));
                            %pi  %pi  5 %pi  13 %pi  9 %pi  13 %pi
         (%o17)            [---, ---, -----, ------, -----, ------]
                            12    8     8      12      8      8
         (%i18) float(%), numer;
         (%o18) [0.2617993877991494, 0.3926990816987241, 1.963495408493621,
                               3.403392041388942, 3.534291735288517, 5.105088062083414]

     Answer: \(x = a + 2\pi k,\) where a any from S, k any integer.

  3.     (%i19) eq:8*cos(x)*cos(4*x)*cos(5*x)-1=0;
         (%o19)               8 cos(x) cos(4 x) cos(5 x) - 1 = 0

         (%i20) trigrat(%);
         (%o20)          2 cos(10 x) + 2 cos(8 x) + 2 cos(2 x) + 1 = 0

     Left side is periodic with period \(T=\pi.\)

     We have 10 solutions from [0, pi].

         (%i21) plot2d([lhs(eq),rhs(eq)],[x,0,%pi]);

         (%i22) x4:find_root(eq, x, 1.3, 1.32);
         (%o22)                        1.308996938995747
         (%i23) x5:find_root(eq, x, 1.32, 1.35);
         (%o23)                        1.346396851538483
         (%i24) plot2d([lhs(eq),0], [x,1.3,1.35], [gnuplot_preamble, "set grid;"]);

     Equation we multiply by \(2\sin x\cos 2x:\)

         (%i25) eq*2*sin(x)*cos(2*x);
         (%o25)     2 sin(x) cos(2 x) (8 cos(x) cos(4 x) cos(5 x) - 1) = 0
         (%i26) eq1:trigreduce(%),expand;
         (%o26)                     sin(13 x) + sin(x) = 0

         (%i27) trigfactor(lhs(eq1))=0;
         (%o27)                     2 cos(6 x) sin(7 x) = 0

         (%i28) S1:trigsolve(cos(6*x),0,%pi);
                             %pi  %pi  5 %pi  7 %pi  3 %pi  11 %pi
         (%o28)             {---, ---, -----, -----, -----, ------}
                             12    4    12     12      4      12

         (%i29) S2:trigsolve(sin(7*x),0,%pi);
                              %pi  2 %pi  3 %pi  4 %pi  5 %pi  6 %pi
         (%o29)           {0, ---, -----, -----, -----, -----, -----}
                               7     7      7      7      7      7

     We remove solutions of \(\sin x = 0\) and \(\cos 2x = 0.\)

         (%i30) S3:trigsolve(sin(x),0,%pi);
         (%o30)                               {0}
         (%i31) S4:trigsolve(cos(2*x),0,%pi);
                                          %pi  3 %pi
         (%o31)                          {---, -----}
                                           4     4

     We find 10 solutions from \([0, \pi]:\)

         (%i32) union(S1,S2)$ setdifference(%,S3)$ setdifference(%,S4);
                  %pi  %pi  2 %pi  5 %pi  3 %pi  4 %pi  7 %pi  5 %pi  6 %pi  11 %pi
         (%o34) {---, ---, -----, -----, -----, -----, -----, -----, -----, ------}
                  12    7     7     12      7      7     12      7      7      12

         (%i35) S:listify(%);
                 %pi  %pi  2 %pi  5 %pi  3 %pi  4 %pi  7 %pi  5 %pi  6 %pi  11 %pi
         (%o35) [---, ---, -----, -----, -----, -----, -----, -----, -----, ------]
                 12    7     7     12      7      7     12      7      7      12

         (%i36) length(S);
         (%o36)                               10
         (%i37) float(S), numer;
         (%o37) [0.2617993877991494, 0.4487989505128276, 0.8975979010256552,
         1.308996938995747, 1.346396851538483, 1.79519580205131, 1.832595714594046,
         2.243994752564138, 2.692793703076966, 2.879793265790644]

     Answer: \(x = a + 2\pi k,\) where a any from S, k any integer.

  Categories: Trigonometric functions · Package trigtools ·

Next: Contract atan Functions, Previous: Solve Trignometric Equations, Up: Functions and Variables for trigtools [Contents][Index]

#### 97.2.6 Evaluation of Trignometric Functions

Function: trigvalue (x)

  The function trigvalue compute values of \(\sin {m\pi\over n},\) \(\cos {m\pi\over n},\) \(\tan {m\pi\over n},\) and \(\cot {m\pi\over n}\) in radicals.

  `trigvalue` is essentially an internal function. Use function `trigeval` in preference.

  `load("trigtools")` loads this function.

Function: trigeval (x)

  The function trigeval compute values of expressions with \(\sin {m\pi\over n},\) \(\cos {m\pi\over n},\) \(\tan {m\pi\over n},\) and \(\cot {m\pi\over n}\) in radicals.

`load("trigtools")` loads this function.

Examples:

1. Values of trignometric functions

       (%i1) load(trigtools)$

       (%i2) trigvalue(sin(%pi/10));
                                         sqrt(5) - 1
       (%o2)                             -----------
                                              4

       (%i3) trigvalue(cos(%pi/10));
                                      sqrt(sqrt(5) + 5)
       (%o3)                          -----------------
                                             3/2
                                            2

       (%i4) trigvalue(tan(%pi/10));
                                     sqrt(5 - 2 sqrt(5))
       (%o4)                         -------------------
                                           sqrt(5)

       (%i5) float(%), numer;
       (%o5)                         0.3249196962329063
       (%i6) float(tan(%pi/10)), numer;
       (%o6)                         0.3249196962329063
       (%i7) trigvalue(cot(%pi/10));
       (%o7)                         sqrt(2 sqrt(5) + 5)
       (%i8) float(%), numer;
       (%o8)                          3.077683537175254
       (%i9) float(cot(%pi/10)), numer;
       (%o9)                          3.077683537175254
       (%i10) trigvalue(sin(%pi/32));
                            sqrt(2 - sqrt(sqrt(sqrt(2) + 2) + 2))
       (%o10)               -------------------------------------
                                              2
       (%i11) trigvalue(cos(%pi/32));
                            sqrt(sqrt(sqrt(sqrt(2) + 2) + 2) + 2)
       (%o11)               -------------------------------------
                                              2
       (%i12) trigvalue(cos(%pi/256));
              sqrt(sqrt(sqrt(sqrt(sqrt(sqrt(sqrt(2) + 2) + 2) + 2) + 2) + 2) + 2)
       (%o12) -------------------------------------------------------------------
                                               2
       (%i13) trigvalue(cos(%pi/60));
               sqrt(sqrt(sqrt(2) sqrt(3) sqrt(sqrt(5) + 5) + sqrt(5) + 7) + 4)
       (%o13)  ---------------------------------------------------------------
                                             3/2
                                            2

       (%i14) trigvalue(sin(%pi/60));
               sqrt(4 - sqrt(sqrt(2) sqrt(3) sqrt(sqrt(5) + 5) + sqrt(5) + 7))
       (%o14)  ---------------------------------------------------------------
                                             3/2
                                            2

       (%i15) trigvalue(sin(%pi/18));
                                              %pi
       (%o15)                             sin(---)
                                              18

       (%i16) trigvalue(sin(%pi/20));
                             sqrt(4 - sqrt(2) sqrt(sqrt(5) + 5))
       (%o16)                -----------------------------------
                                             3/2
                                            2

2. ode example

       (%i17) load(odes)$

       (%i18) eq:'diff(y,x,5)+2*y=0;
                                         5
                                        d y
       (%o18)                           --- + 2 y = 0
                                          5
                                        dx

       (%i19) odeL(eq,y,x);

                          1/5     4 %pi
                       - 2    cos(-----) x
                                    5           1/5     4 %pi
       (%o19) y = C5 %e                    sin(2    sin(-----) x)
                                                          5
                  1/5     4 %pi
               - 2    cos(-----) x
                            5           1/5     4 %pi
        + C4 %e                    cos(2    sin(-----) x)
                                                  5
                  1/5     2 %pi
               - 2    cos(-----) x
                            5           1/5     2 %pi
        + C3 %e                    sin(2    sin(-----) x)
                                                  5
                  1/5     2 %pi
               - 2    cos(-----) x                                  1/5
                            5           1/5     2 %pi            - 2    x
        + C2 %e                    cos(2    sin(-----) x) + C1 %e
                                                  5

       (%i20) sol:trigeval(%);
                         (sqrt(5) - 1) x
                       - ---------------
                               9/5
                              2              sqrt(sqrt(5) + 5) x
       (%o20) y = C3 %e                  sin(-------------------)
                                                    13/10
                                                   2
                 (sqrt(5) - 1) x
               - ---------------
                       9/5
                      2              sqrt(sqrt(5) + 5) x
        + C2 %e                  cos(-------------------)
                                            13/10
                                           2
               (sqrt(5) + 1) x
               ---------------
                     9/5
                    2              sqrt(5 - sqrt(5)) x
        + C5 %e                sin(-------------------)
                                          13/10
                                         2
               (sqrt(5) + 1) x
               ---------------
                     9/5                                          1/5
                    2              sqrt(5 - sqrt(5)) x         - 2    x
        + C4 %e                cos(-------------------) + C1 %e
                                          13/10
                                         2

       (%i21) subst(sol,eq)$
       (%i22) ev(%, nouns)$
       (%i23) radcan(%);
       (%o23)                               0 = 0

3. n-th root of complex number

   Example. Find the 4-th roots of %i

       (%i24) solve(x^4=%i,x);
                        1/8                1/8             1/8              1/8
       (%o24) [x = (- 1)    %i, x = - (- 1)   , x = - (- 1)    %i, x = (- 1)   ]

       (%i25) rectform(%);
                          %pi        %pi                 %pi         %pi
       (%o25) [x = %i cos(---) - sin(---), x = (- %i sin(---)) - cos(---),
                           8          8                   8           8
                                       %pi           %pi              %pi        %pi
                               x = sin(---) - %i cos(---), x = %i sin(---) + cos(---)]
                                        8             8                8          8

       (%i26) trigeval(%);
                   sqrt(sqrt(2) + 2) %i   sqrt(2 - sqrt(2))
       (%o26) [x = -------------------- - -----------------,
                            2                     2
              sqrt(2 - sqrt(2)) %i    sqrt(sqrt(2) + 2)
       x = (- --------------------) - -----------------,
                       2                      2
           sqrt(2 - sqrt(2))   sqrt(sqrt(2) + 2) %i
       x = ----------------- - --------------------,
                   2                    2
           sqrt(2 - sqrt(2)) %i   sqrt(sqrt(2) + 2)
       x = -------------------- + -----------------]
                    2                     2

Categories: Trigonometric functions · Package trigtools ·

Previous: Evaluation of Trignometric Functions, Up: Functions and Variables for trigtools [Contents][Index]

#### 97.2.7 Contract atan Functions

Function: atan_contract (r)

  The function atan_contract(r) contracts atan functions. We assume: \(|r| < {\pi\over 2}.\)

  `load("trigtools")` loads this function.

  Examples:

      (%i1) load(trigtools)$

  1.     (%i2) atan_contract(atan(x)+atan(y));
         (%o2)                          atan(y) + atan(x)
         (%i3) assume(abs(atan(x)+atan(y))<%pi/2)$
         (%i4) atan(x)+atan(y)=atan_contract(atan(x)+atan(y));
                                                          y + x
         (%o4)                  atan(y) + atan(x) = atan(-------)
                                                         1 - x y

  2.     (%i5) atan(1/3)+atan(1/5)+atan(1/7)+atan(1/8)$ %=atan_contract(%);
                                1         1         1         1    %pi
         (%o6)             atan(-) + atan(-) + atan(-) + atan(-) = ---
                                3         5         7         8     4

  3. Machin’s formulae

         (%i7) 4*atan(1/5)-atan(1/239)=atan_contract(4*atan(1/5)-atan(1/239));
                                          1          1     %pi
         (%o7)                     4 atan(-) - atan(---) = ---
                                          5         239     4

  4. see http://en.wikipedia.org/wiki/Machin-like_formula

         (%i8) 12*atan(1/49)+32*atan(1/57)-5*atan(1/239)+12*atan(1/110443)$
         %=atan_contract(%);
                         1             1             1               1       %pi
         (%o9)   12 atan(--) + 32 atan(--) - 5 atan(---) + 12 atan(------) = ---
                         49            57           239            110443     4

  Categories: Trigonometric functions · Package trigtools ·

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### 97.3 References

1. http://maxima.sourceforge.net

#### Footnotes

### (10)

This is a conversion by hand of the original “trigtools-doc.pdf” file in “share/contrib/trigtools”, by Raymond Toy. See the pdf for the definitive version.

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