Ellipse chord joining two points subtends an angle identity can't understand the Ques

Show that an equation of the chord joining the points P$\displaystyle (acos\omega, bsin\omega)$ and Q$\displaystyle (acos\theta, b sin\theta)$ on the ellipse with equation $\displaystyle b^2x^2+a^2y^2=a^2b^2$ is

$\displaystyle Bxcos\frac{1}{2}(\theta+\omega)+aysin{1}{2}(\theta +\omega)=abcos{1}{2}(\theta-\omega)

$(SOLVED)

“Prove that, if the chord PQ subtends a right angle at the point (a,0), then PQ passes through a fixed point on the x-axis.”

The part in the quotation, I cannot understand what it demands, let alone do it. Will be gratified if somebody comes forward with a more graphic explanation. Help