1. The problem statement, all variables and given/known data I need to prove that a 4x4 matrix has 2 zero eignenvalues. 2. The attempt at a solution I have tried to obtain the characteristic equation but calculating the determinant of a relevant 4x4 is rather daunting as there aren't many zeros. I was wondering if there is any other way to prove the statement without resorting to this brute force approach. Thank you in advance!