SRL Archive - Mathematics

Finding this question part a bit hard to do. It is part 3 (one in the red box)

If anyone knows how to prove it and could explain, it would be most helpful indeed.

Thanks in advance :)

I did the first part of that part of the question (prove f(x+pi))(see attached). Since people complain about my handwriting I typed it up. Last time I had calc was 2 years ago. So I don't remember u substitution.

PS: Didn't really take the time to check my typing, so don't just copy it.