Hi I'm not sure if this is the right forum to post this, but if it is not, I sincerely apologize.

I am really stuck at these two questions,

1.) Find all 2x2 matrices A for which A^2=A by letting A = $\displaystyle \begin{pmatrix} a & b \\c & d \end{pmatrix}$

This was the last part to this question, "The result "If ab=0 then a=0 or b=0 for real numbers does not have an equivalent result for matrices."

I don't know if this could be helpful but I really do not know how to do this question..

2.) Give one example which shows that if "A^2=O then A=O" is a false statement. (O is the null matrix!)

I got up to multiplying the matrices together and then equated it to 0..

Really appreciate your help!