PQ is the focal chord of parabola y^2=4ax. the tangents at P and Q meet at line y=2x+a. a>0. If chord subtends an angle theta at vertex of the parabola. find tan theta.
I got the answer as 2√5/3 but it says -2√5/3, which means the angle is obtuse. why is it so? as acc to the formula tan theta=|m1-m2/1+m1m2|, the ans should always be +ve