A square + b square by a b equals to 25 by 12 prove that a cube minus b cube by a cube plus b cube?

"By" is not a recognized math statement.

We use Shift-6 for powers, like this: A^2

Get out of the habit of hitting Shift just because you start a new line. A is not a and a math program will not tell you that you made a mistake. It will just give goofy results.