Hello to everyone

I have a question with many parts that i am needing to do.

(a)Derive the 2point formula, for numerical differentiation:

What is ?

(b) Derive the same formula as (b) witht 3points formula

(c) Discretisation error in (a) and (b) is

Prove that discretisation error for f'(1), where f(x) = exp(x) is

I am knowing that

but I cannot realise how to do these parts? Can someone please showing me how to prove?