You may let x be tan(x), then form a quadratic equation to solve for x. Then tan(x)=2 or -2. Find principal angle by tan^-1(2). Determine which quadrant it lies on from the range. Answers to be in radians as given in the domain by the question. You may also visualize it using the graphical representation (draw the tangent graph and see where 2 or -2 cuts the tangent curve). Hope it helps!