Let $A = \left[\begin{array}{ccc} 11 &0 &-20\cr 4 &1 &-8\cr 6 &0 &-11 \end{array}\right]$. Find an invertible matrix $P$ and a diagonal matrix $D$ such that $D = P^{-1}AP$.
$P=$ $\left[\Rule{0pt}{3.6em}{0pt}\right.$$\left]\Rule{0pt}{3.6em}{0pt}\right.$, $D=$ $\left[\Rule{0pt}{3.6em}{0pt}\right.$$\left]\Rule{0pt}{3.6em}{0pt}\right.$