# Thread: Polar form double integral

1. ## Polar form double integral

The question

I have the region $\displaystyle x^2 + (y - 1)^2 = 1$ which is a circle above the x-axis.

I want to describe using polar co-ordinates, but I'm a little stuck. I realise that it goes from 0 to Pi, but the behaviour of the radius I'm not sure of.

Any assistance would be great!

2. Just plug in the usual substitution and simplify. What do you get?

3. What do you mean by usual substitution?

4. Seriously?

$\displaystyle x = r\cdot\cos(\theta)$

$\displaystyle y = r\cdot\sin(\theta)$

$\displaystyle x^{2} + y^{2} = r^{2}$

5. Originally Posted by TKHunny
Seriously?

$\displaystyle x = r\cdot\cos(\theta)$

$\displaystyle y = r\cdot\sin(\theta)$

$\displaystyle x^{2} + y^{2} = r^{2}$
Thank you, but you could have refrained from using such a condescending tone. If I knew what the "usual substitution" was, then I wouldn't have asked the question in the first place.

Anyway, is the solution $\displaystyle r = 2sin(\theta)$?

6. Originally Posted by Glitch
Anyway, is the solution $\displaystyle r = 2sin(\theta)$?
That's what I get.

7. Originally Posted by Glitch
Thank you, but you could have refrained from using such a condescending tone.
I do have trouble with that. We all have little holes in our education. Some are just a little more out of place than others and they strike me as odd.