Let's start with the first question. Is to regard √x as a whole, then X=√x?

f(x)=x2+2x- 1

Think of the brackets as a whole, and then make them in the same form.

In fact, just set the brackets to t and solve X=? I hope t brought it in.

For example, the second question: let T=X- 1, then X=T+ 1, then f(t)=(t+ 1)? That is f(x)=(x+ 1)?

This solution is very fast.