Equation of OP:- y = x tan α Solving with y2=4ax, we get : x2tan2α=4ax⇒x=4acot2α Substituting, y = 4a cot α ∴P=(4acot2α,4a‌cot‌α) So, OP=√16a2cot4α+16a2cot2α=4a‌cot‌α‌cosec‌α (as 0° < α < 90°, so, cot α > 0, cosec α > 0)