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#821 csc & trigexpand

closed
nobody
Lisp Core (472)
5
2005-12-09
2005-11-30
Barton Willis
No

I think trigexpandtimes with csc is buggy:

(%i59) csc(3*x),trigexpand;
(%o59) (csc(x)^3*sec(x)^3)/(3*csc(x)*sec(x)^2-csc(x)
^3)
(%i60) %-csc(3*x);
(%o60) (csc(x)^3*sec(x)^3)/(3*csc(x)*sec(x)^2-csc(x)
^3)-csc(3*x)
(%i61) subst(x=0.3,%);
(%o61) -2.8853320239249447 <-- should be zero.

Barton

Discussion

  • Raymond Toy
    Raymond Toy
    2005-11-30

    • labels: --> Lisp Core
     
  • Raymond Toy
    Raymond Toy
    2005-11-30

    Logged In: YES
    user_id=28849

    In csc\Sec-times, the last lines says

    \(sin\Cos-times l m n f1 f2 flag\)\)\)
    

    If we swap f1 and f2 like so:

    \(sin\Cos-times l m n f2 f1 flag\)\)\)
    

    With this change:

    (%i35) csc(3*x),trigexpand;

    (%o35) csc(x)^3*sec(x)^3/(3*csc(x)^2*sec(x)-sec(x)^3)
    (%i36) ev(%-csc(3*x),x=0.3);

    (%o36) -6.661338147750939e-16

    This looks better.

     
  • Raymond Toy
    Raymond Toy
    2005-12-09

    Logged In: YES
    user_id=28849

    Suggested fix applied.

     
  • Raymond Toy
    Raymond Toy
    2005-12-09

    • status: open --> closed