\(\displaystyle y = \sqrt {r^2 - x^2 }\) is a semi circle centered at the origin with radius r.
If (p,q) is point on the semi circle then \(\displaystyle p^2 + q^2 = r^2\)
Show that the line through the (p,q) and (−r,0) is perpendicular to the line through (p,q) and (r,0).