If a parabolic reflector is 20 cm in diameter and 5 cm deep, find the focus.

The equation of the parabola is of the formy²= 4ax(as it is opening to the right).

Since the parabola passes through point A (10, 5), 10²= 4a(5)

100 = 20a

Therefore, the focus of the parabola is (a, 0) = (5, 0), which is the mid-point of the diameter.

Hence, the focus of the reflector is at the mid-point of the diameter.