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Given A = $\begin{bmatrix} 1 &2 &2 \\ 2&1 &-2 \\ a&2 &b \end{bmatrix}$

And AAAT = 3I

I is a 3x3 identity matrix.

(a,b) can be:

A. (2,-1)

B. (-2,1)

C. (-2,-1)

D. (2,1)

How to solve it fast?

1 Answer

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Simple,first find determinant of matrix which is  -3b-6a+12 then select the value of a and b which will give you value 3

only option a satify the requirement .so ans is a.

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