Here's the question.

If P is any point on the hyperbola and PR and PS are drawn parallel to the asymptotes, the dPR x dPS = constant. Show this is true for the hyperbola:

x^2/4 - y^2/4 = 1

by choosing three different points for P. Can you prove the general case?

P.S. I'm assuming that dPR means the distance from P to R.

Here's the diagram

Thanks in advance.