I need help with 1 - 4 please

Atriangle has a side lengths of 18cm, 80 cm and 81cm. classify it as acute obtuse or right?

Do you mind if you guys me with this question i’m on number 8

To diagonalize an nxn matrix a means to find an invertible matrix p and a diagonal matrix d such that a pdp d p ap or [1 3 dh epap 3 let a=-3 -5 -3 3 3 1 step 1: find the eigenvalues of matrix a "2's" step 2: find the corresponding eigenvectors of a step 3: createp from eigenvectors in step 2 step 4 create d with matching eigenvalues.