F.4 A.Maths

Let f(x)=aX^2+bx+c,where a,b,c are real and a not=0
If Alpha and Bravo are the roots of f(x)-x=0,prove that Alpha and Bravo also
the roots of f[f(x)]


If f(x)=x^2-3x+2,solve f[f(x)]-x=0