00:01
Okay, in this question we want to show this series, n from 1 to positive infinity, cosine nx over n to the power 2.
00:17
We want to show this uniformly convergent.
00:20
We use the double arrow to represent the uniform convergence.
00:26
This uniformly converges to some function fx, and f is continuous r.
00:37
This is our goal.
00:40
Now for any natural number k, let's define f sub kx, let's define this as the summation from 1 to k cosine nx over n squared.
01:01
We know for each k, f has its finite sum and by the continuity of the cosine function, continuous function on r.
01:18
This is true for any k.
01:21
Okay, that means if we can show f converges uniformly to some g then this g must be continuous.
01:42
This is a property of the uniform convergence.
01:47
Once the uniform convergence can guarantee, the uniform convergence implies the continuity of the limit function.
01:57
Function.
01:58
But you know the limit of f , the pointwise limit of f is just equal to n from 1 to positive infinity...