Thread: Matrices det (a)=0

The question is that i shall find all numbers for a so that det (A)=0
i basicly dont know what trick i shall use!
edit: i did start to det it and set it to zero but i get wrong

First find the determinant using cofactor expansion method.

yes i did it.. i get -2a^2+10a-20 and then i set it to zero and get the answer
a=25
a=-10
the answe shall be 3 and 2 but idk what i do wrong =S

Originally Posted by Petrus

The question is that i shall find all numbers for a so that det (A)=0
i basicly dont know what trick i shall use!
edit: i did start to det it and set it to zero but i get wrong

Expand these and solve for a.

Originally Posted by Plato

Expand these and solve for a.

so im basicly pretty new on matrice :P ik how to expaned but why did u do it? and why cant we use sorrow rule or what the name to find det on 3x3 matrice?

Originally Posted by Petrus

so im basicly pretty new on matrice :P ik how to expaned but why did u do it? and why cant we use sorrow rule or what the name to find det on 3x3 matrice?

I have no idea what the meaning of that may be.

You should get and answers .