Given that tan(2A) = (2tanA)/(1-tan^2 A)
show that tan(22.5) = sqrt(2) - 1
You have the correct quadratic...now either complete the square or use the quadratic formula.
You will get 2 roots. You will need to decide which is extraneous, either by substituting the roots into the original equation, or some knowledge of which quadrant the angle is in and what sign tangent has there...