If A is a 2X2 matrix, a12 = a21 = 0, a11 ≠ 0, a22 ≠ 0 then show that A is regular and find A^-1.

Many thanks in advance.

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- Jan 31st 2011, 05:23 PMgrooverandshakerMatrix question.
If A is a 2X2 matrix, a12 = a21 = 0, a11 ≠ 0, a22 ≠ 0 then show that A is regular and find A^-1.

Many thanks in advance. - Jan 31st 2011, 05:35 PMtopsquark
- Jan 31st 2011, 05:41 PMgrooverandshaker
Um, I know that a matrix has an inverse if the determinant is nonzero. Is that right?

I usually know how to find the determinant and the inverse but I just can't do it when the matrix isn't written out.

Could you help me figure out what the original matrix is? - Jan 31st 2011, 06:00 PMrtblue
Given that a12 and a21 are both 0 and that a11 and a22 are not 0, the matrix must have a nonzero determinant. There are no values of a11 and a22 that can make the determinant 0.

- Jan 31st 2011, 06:13 PMtopsquark

This page seems to be a good guide in general. It has an explicit answer for the 2 x 2 case, but make sure you understand how to do the problem in general.

-Dan - Jan 31st 2011, 07:11 PMdwsmith

- Jan 31st 2011, 09:53 PMgrooverandshaker
Thanks guys. I think I understand now. :D