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

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- Nov 29th 2012, 10:29 AMPetrusMatrices 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 - Nov 29th 2012, 11:11 AMScopurRe: Matrices det (a)=0
First find the determinant using cofactor expansion method.

- Nov 29th 2012, 11:24 AMPetrusRe: Matrices det (a)=0
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 - Nov 29th 2012, 11:25 AMPlatoRe: Matrices det (a)=0
Expand these and solve for a.

$\displaystyle 2\left| {\begin{array}{rr} a & 1 \\ 2 & {2a + 2} \\ \end{array} } \right| - \left| {\begin{array}{rr} { - 2} & 1 \\ {2a} & 2 \\ \end{array} } \right| + 3\left| {\begin{array}{rr} { - 2} & a \\ a & 2 \\ \end{array} } \right| = 0$ - Nov 29th 2012, 11:30 AMPetrusRe: Matrices det (a)=0
- Nov 29th 2012, 11:48 AMPlatoRe: Matrices det (a)=0