Question is:

The variable chord $\displaystyle PQ$ on the parabola with equation $\displaystyle y^2=4x$ subtends a right angle at the origin $\displaystyle O$. By taking $\displaystyle P$ as $\displaystyle (t_1^2,2t_1)$ and $\displaystyle Q$ as $\displaystyle (t_2^2,2t_2)$, find a relation between $\displaystyle t_1$ and $\displaystyle t_2$ and hence show that $\displaystyle PQ$ passes through a fixed point on the $\displaystyle x-axis$.