koni then what's with my solution, I mean the function I got was

 

f(x)=x²/2 if you substitute it in your sol. you get

 

(x+1)² /2= x²/2 + x

 

=> x² + 2x + 1 = x² + 2x

 

then what's wrong??? you also have said that f(1)=1 but by my sol.

 

f(1) =1/ 2 ?? And how did you get the value of f(1)?