00:01
So we're gonna look at the radius and interval of convergence of some power series.
00:06
So this one, i recognize it as being the derivative of a geometric series.
00:17
There's actually, you have to multiply through by z to get our answer, z out in front here.
00:29
But that's gonna, i'll correct that when we get to the end.
00:39
So that's a geometric series.
00:41
Its radius of convergence is one, and taking the derivative doesn't affect that, and our interval is minus one less than z less than one, because the geometric series never includes the endpoints either.
00:59
Second one, this is not a geometric series.
01:05
We can use the ratio test.
01:12
Can factor out an x over four.
01:17
We get that limit, which is one...