Cheer up,

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

therefore

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

or

Let x- 1=t,

x=t+ 1

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

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