The time of the video will give you the answer
5:31
Nice "alternative method" (the long way)
5:18
Overkill it with multiple methods!
22:22
10,000 Problems in Analysis
18:39
Can you crack this beautiful equation? – University exam question
6:18
Specific example of a nice general form
8:42
The Intuition behind Hilbert Spaces and Fourier Series
12:31
Possible vs Reasonable
1:55:27