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Y=cosx is decreasing

  • Thread starter rocomath
  • Start date
  • #1
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Hmm ... I did this problem for a friend.

From what x values is [tex]y=cos x[/tex] decreasing from [tex]-\pi\leq x\leq\pi[/tex]

http://img440.imageshack.us/img440/3876/baocu5.jpg [Broken]​
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*it should be [tex]-\frac{\pi}{2} \ \mbox{not} \ -\frac{3\pi}{2}[/tex]

It's decreasing from [tex](0,\pi)[/tex] but the answer she gave me from the back of the book is [tex]-\frac{3\pi}{2}<x<\frac{3\pi}{2}[/tex]
 
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Answers and Replies

  • #2
1,750
1
Nvm ... we apparently moved onto a different question, lol.
 
  • #3
1,341
3
The book's wrong
 
  • #4
360
21
Must be some of that new math :confused:
 
  • #5
1,750
1
The book's wrong
LOL, no she started asking about a different question ... I just didn't realize, ha. I was like wtf ... b/c the answer she gave me wasn't even in the interval they were asking about! haha, I kept saying no it's wrong! And I'll prove it by asking the PF Gods :)
 
  • #6
1,341
3
It looks a bit wierd when it askes for the answer on the interval [-pi,pi] the books gives the answer as [-1.5pi,1.5pi]
 

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