Originally Posted by

**rorosingsong** Hiya, I'm stuck on this question and would be really grateful if someone could help me out here...

Let $\displaystyle M = \begin{bmatrix}7 & -3\\15 &-7 \end{bmatrix}$. Find all 2x2 matrices $\displaystyle A = \begin{bmatrix}a & b\\b &d \end{bmatrix}$ such that AM = - MA. (Note that the solutions wanted should have equal (1,2)- and (2,1)- entries b.)

I tried evaluating the equation AM= -MA via matrix multiplication and making equations out of the corresponding entries but ended up with something that just seemed completely wrong AND didn't have equal (1,2)- and (2,1)- entries.

Please help! Thanks in advance,

rorosingsong.