Question

If A=$\left[\begin{array}{ccc}1&-2\\2&-1\\\end{array}\right]$, B=$\left[\begin{array}{ccc}a&1\\b&-1\\\end{array}\right]$ and $(A+B)^{2}=A^{2}+B^{2},$, Find a and b.

Answer 1

They are right aligned because you have {array}{lr} change that to {array}{ll} to left align both columns. But generally it is best not to use array for laying out whole equations, it is designed for matrices/arrays. Here I think the amsmath package and its cases environment would be better.

HOPE IT HELPS ✌

Answer 2

my frnd's answer is right