http://img409.imageshack.us/img409/2644/matrixnh4.jpg

A.) Determine the characteristic polynomial and characteristic roots of A.

For this, I got $\displaystyle X^2-6X+8 $ and Roots: X=4 and X=2

I'm not sure what to do for the next part.

B.) Find a nonsingular matrix P and diagonal matrix D such that $\displaystyle P^{-1}*AP= D$.