## A community for students. Sign up today

Here's the question you clicked on:

## allsmiles 2 years ago Evaluate ∫∫ over D (cos(sqrt(x^2+y^2)) dA by changing polar coordinates where the disk is with center of origin and radius 2

• This Question is Closed
1. allsmiles

I got up to ∫∫[0 to 2pi] [0 to 2] cos(sqrt(r)) r dr dt

2. allsmiles

but I can't solve for it! How do integrate r*cos(sqrt(r))

3. myko

$\int\limits\int\limits_{D}=\int\limits_{0}^{2\pi} d\theta\ \int\limits_{0}^{2}r \cos rdr$

4. allsmiles

omg you are correct.

5. allsmiles

spent literally 30 mins trying to see what I did wrong. That was quick thanks a lot man

6. myko

yw

7. myko

by the way:int( rcos r) it's done by integration by parts

8. allsmiles

can't I do substitution

9. myko

you can try

10. allsmiles

haha I just did and it didn't work, alright thanks again!

11. myko

if you have problems look here, :) http://en.wikipedia.org/wiki/Integration_by_parts

12. myko

there exacly you example

13. myko

your*

14. allsmiles

Yeah I got it now, thanks a lot for your help!

#### Ask your own question

Sign Up
Find more explanations on OpenStudy
Privacy Policy