# Y=cosx is decreasing

1. Mar 30, 2008

### rocomath

Hmm ... I did this problem for a friend.

From what x values is $$y=cos x$$ decreasing from $$-\pi\leq x\leq\pi$$

*it should be $$-\frac{\pi}{2} \ \mbox{not} \ -\frac{3\pi}{2}$$

It's decreasing from $$(0,\pi)$$ but the answer she gave me from the back of the book is $$-\frac{3\pi}{2}<x<\frac{3\pi}{2}$$

Last edited: Mar 30, 2008
2. Mar 30, 2008

### rocomath

Nvm ... we apparently moved onto a different question, lol.

3. Mar 30, 2008

### Feldoh

The book's wrong

4. Mar 30, 2008

### montoyas7940

Must be some of that new math

5. Mar 31, 2008

### rocomath

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. Mar 31, 2008

### Feldoh

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]