00:01
So here we need to evaluate the integral from pi over 4 to pi over 2, integral from 0 to 4 over sine theta of r squared coast theta, drd theta.
00:11
You already figured out this first part, and it looks like you just need to evaluate this integral.
00:18
So first off, we can evaluate the r integral.
00:22
There's no real problem there.
00:24
So we still have the theta integral on the outside, and we leave the coast data here.
00:28
We treat it as a constant, and then the integral of r squared is just r cubed over 3, and we want to evaluate that from 0 to 4 over sine theta.
00:38
So we don't have to worry about 0 when we plug in 0 for r, we get 0.
00:43
So that just gives us a factor of 4 cubed from the r cubed, and then we'll also have a 1 over sine cubed theta from that.
00:51
So now we have the integral of coast theta over sine cubed theta d theta, which looks really tricky at first...