On number one, substitute the two answers you got back into the original equation (note that only one works for real numbers). Your answer to number two looks right to me. As for number three, factor out :
So either x=0 or . Note that as , this is quadratic in . If we let , this becomes , which is easily factorizable; note that must be positive, so only one of the roots of that quadratic will square to give an x that solves the original equation.