Post Reply 
Trig Error in CAS
02-12-2016, 06:42 PM (This post was last modified: 02-12-2016 07:06 PM by chazzs.)
Post: #1
Trig Error in CAS
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
Find all posts by this user
Quote this message in a reply
02-12-2016, 10:19 PM (This post was last modified: 02-12-2016 10:21 PM by DrD.)
Post: #2
RE: Trig Error in CAS
Wolfram says: http://www.wolframalpha.com/input/?i=aco...%284%29%29

Here is my screenshot (Exact mode toggled):


Attached File(s) Thumbnail(s)
   
Find all posts by this user
Quote this message in a reply
02-13-2016, 12:30 AM
Post: #3
RE: Trig Error in CAS
Interesting. Here's my screenshot.    
Find all posts by this user
Quote this message in a reply
02-13-2016, 03:29 AM (This post was last modified: 02-13-2016 09:15 PM by compsystems.)
Post: #4
RE: Trig Error in CAS
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?
Find all posts by this user
Quote this message in a reply
Post Reply 




User(s) browsing this thread: 1 Guest(s)