# Xy coordinates to polar coordinates for double integral. hepl please!

by Andrew123
Tags: coordinates, double, hepl, integral, polar
 P: 25 1. The problem statement, all variables and given/known data ok change the region R = { (x,y) | 1 <= X^2 + y^2 <= 4 , 0 <= y <= x } to polar region and perform the double integral over region R of z=arctan(y/x)dA 2. Relevant equations r^2 = x^2 + y^2, x = r*sin(@), y = r * cos (@) 3. The attempt at a solution i got R = { (rcos(@), rsin(@) | 1 <= r <= 2 , 0 <= @ <= pi/4 } and 3/8 * pi ^2 answer in back of book is 3/64 * pi ^2 thankyou for your time!
HW Helper
P: 5,003
 Quote by Andrew123 1. The problem statement, all variables and given/known data ok change the region R = { (x,y) | 1 <= X^2 + y^2 <= 4 , 0 <= y <= x } to polar region and perform the double integral over region R of z=arctan(y/x)dA 2. Relevant equations r^2 = x^2 + y^2, x = r*sin(@), y = r * cos (@) 3. The attempt at a solution i got R = { (rcos(@), rsin(@) | 1 <= r <= 2 , 0 <= @ <= pi/4 } and 3/8 * pi ^2 answer in back of book is 3/64 * pi ^2 thankyou for your time!
You've correctly converted to polar coordinates and found the limits of integration, but you somehow made a mistake evaluating the integral...Did you by chance forget that you are integrating the function $\tan^{-1}\left(\frac{y}{x}\right)=\theta$ over this region, andf just find the area of the region instead?
 P: 25 thankyou veeery much!
Mentor
P: 21,261
Xy coordinates to polar coordinates for double integral. hepl please!

 Quote by Andrew123;2056564[b 2. Relevant equations[/b] r^2 = x^2 + y^2, x = r*sin(@), y = r * cos (@)
Not sure this made a difference in your answer, but the equations for x and y above are wrong. They should be
x = r*cos(theta)
y = r*sin(theta)

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