Find the eigenvalues of {{2,6,-15},{1,1,-5},{1,2,-6}}
According to wolframalpha i should be getting λ1,2,3=-1, but i keep getting λ1,2,3=3 as a solution. Can someone tell me what's wrong?
My last line of the equation is: - λ^3-3* λ^2+7* λ-21=0...

Question

Find the eigenvalues of {{2,6,-15},{1,1,-5},{1,2,-6}}
According to wolframalpha i should be getting  λ1,2,3=-1, but i keep getting  λ1,2,3=3 as a solution. Can someone tell me what's wrong?
My last line of the equation is: - λ^3-3* λ^2+7* λ-21=0...

anonymous · Answer

reduce the form to Jordan normal form, you will have {1,0,0}{0,1,0}{0,0,1} so eigenvalues are -1

anonymous · Answer

Thanks, may i ask if this is always necessary in the case of 3x3 (or larger) matrices?
During classes we only did some basic 2x2 ones, so i'm in the dark for 3x3+ , however on the first (very easy) 3x3 we had as homework, it was all good (even according to wolframalpha) without reducing it to Jordan normal form.