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Trig Error in CAS - chazzs - 02-12-2016 06:42 PM
Can anyone explain to me (or recreate the bug) why acos(cos(2)) = 2pi - 2, and not 2, which you get when evaluating acos(cos(2.)). Works fine on the home side.
It seems 1 is the only (integer) value that is correct: acos(cos(1))=1.
Worse is acos(cos(4)) = -2 pi + 4 = -2.2831 (Should be positive, or 2 pi - 4).
These are all in radian mode. Degree mode seems to work fine. A little troubling, or I'm missing something.
C
RE: Trig Error in CAS - DrD - 02-12-2016 10:19 PM
Wolfram says: http://www.wolframalpha.com/input/?i=acos%28cos%284%29%29
Here is my screenshot (Exact mode toggled):
RE: Trig Error in CAS - chazzs - 02-13-2016 12:30 AM
Interesting. Here's my screenshot.[attachment=3125]
RE: Trig Error in CAS - compsystems - 02-13-2016 03:29 AM
HOME MODE (CNES ): Computer Numeric Expert System
ACOS(COS(4)) [ENTER] 2.28318530718 ok
acos(cos(4)) [ENTER] 2.28318530718 ok
CAES MODE: Computer Algebra Expert System
flag on: Simplify Maximum
ACOS(COS(4)) [ENTER] -2*π+4 approx(Ans) −2.28318530718 ?
acos(cos(4)) [ENTER] -2*π+4 approx(Ans) −2.28318530718
SUGGESTION FOR THE FOLLOWING FIRMWARE
for CAS mode, show history with 2 outputs (Exact result & Decimal Approximation) , as does wolfram CAS
ACOS(COS(4)) [ENTER]
____________________ 2*π-4
____________________ 2.28318530718
Is a good idea?