Converting polar to cartesian coordinates

[bobsmith76]

Homework Statement

Homework Equations

The Attempt at a Solution

Do you see that 2 between A and the integral? There's no 2 in the above equation. I don't see where that 2 came from. Everything else is fine.

 

[Ninty64]

The 2 comes from the symmetry. 0 to pi/4 on the sine circle is only calculating the bottom-right half of the area.

 

[jaqueh]

because if you just did it with no 2*the integral then you would only get the area of half of your region