### Find an invertible matrix ( mathrm{P} ) and a matrix ( mathrm{C} ) of the form ( left[begin{array}{rr}mathrm{a} & -mathrm{b} \ mathrm{b} & mathrm{a}end{array}right] ) such that ( mathrm{A}=left[begin{array}{rr}1 & -26 \ 1 & 11end{array}right] ) has the form ( mathrm{A}=mathrm{PCP}-1 ). The eigenvalues of ( mathrm{A} ) are (

Find an invertible matrix ( mathrm{P} ) and a matrix ( mathrm{C} ) of the form ( left[begin{array}{rr}mathrm{a} & -mathrm{b} \ mathrm{b} & mathrm{a}end{array}right] ) such that ( mathrm{A}=left[begin{array}{rr}1 & -26 \ 1 & 11end{array}right] ) has the form ( mathrm{A}=mathrm{PCP}-1 ). The eigenvalues of ( mathrm{A} ) are (