Known: f (radical x)+ 1=x+2 radical x.

Find f(x)

Solution: f (radical x)+ 1=x+2 radical x.

T= free radical x

f(t)+ 1=t^2+2t

f(t)=t^2+2t- 1

f(x)=x^2+2x- 1

Because you need to ask for f(x), but the known conditions do not directly tell you what f(x) is, and there is an f (radical x) in the title, so you should put f (? ) the thing in brackets is set to t, and then you get an equation. Then you work out X, and then you go back and eliminate all the X in the question. As long as you keep the t you exchanged, you can get the equation f (t) = t 2+2t- 1, but people are used to using x to represent the unknown of the equation, so it is written as f (x) = x 2. The whole process is actually to replace a large string in brackets. The whole string can be an unknown number, but it looks inconvenient and should be replaced by letters.

If you still don't understand, please ask me again