00:01
Okay, so in this problem, theta is the variable.
00:05
So if it's confusing, to you make all the theta's into x's.
00:09
And this is a definite integral, so we'll get a number for the answer.
00:14
So we'll let you be theta, and then dv will be the sign of 3 pi theta, d theta.
00:25
And i put that in parentheses so you know that's the thing i'm taking the sign of.
00:30
So take the derivative, derivative of theta, d theta.
00:34
On this one, integrate v equals.
00:39
Okay, this is a sign of u.
00:41
So du, if u is 3 pi theta, then du would be 3 pi d theta.
00:50
So we have the d theta, so we need a 3 pi, which puts a 1 over 3 pi out here.
00:57
So 1 over 3 pi times the integral of the sign of u, which would be minus the cosine of you.
01:04
So now we get minus 1 over 3 pi theta times the cosine of 3 pi theta minus the integral vdu, which makes plus 1 over 3 pi, integral of the cosine of 3 pi theta d theta.
01:29
The whole thing is 0 to 1 half, although i'm not ready for that yet, but i just wrote it so i wouldn't forget to do it.
01:37
All right, so minus 1 over 3 pi theta, cosine 3 pi theta...