00:01
Section 8 .4, problem number 8.
00:04
So we're dealing with integrals that require a trig substitution.
00:08
So integral 0 to 3 halves, dx 9 minus x squared to the 3 halves power.
00:15
So the substitution to make in this case is to let x equal 3 sine of theta.
00:25
Then it follows that dx would be equal to 3 cosine of theta.
00:33
And then let's work on 9 minus x squared to the three halves.
00:40
That's going to be 9.
00:43
And then when you square x, it's going to be, what, 9 sine squared.
00:47
So this is going to end up being 9.
00:50
1 minus the sine squared of theta to the 3 halves.
00:57
So this is 9 to the 3 halves, cosine squared of theta to the 3 halves.
01:06
So this ends up being, what, 27 cosine to the cubed power of theta.
01:16
So when, now let's just change the limits of integration.
01:20
When x is equal to zero, we have to look right here.
01:25
That means that the sine of zero, that means that zero is equal to three sine of theta, which tells me that theta is equal to zero.
01:36
So when x is equal to three halves, it tells me three halves is equal to three.
01:46
Sin theta, so sine of theta is one -half.
01:50
So theta is equal to pi over six...