The intensity of light varies inversely as the square of the distance from its source. If two searchlights are 600 meters apart and one light is 8 times as strong as the other, where should a man cross the line between them in order to be illuminated as little as possible

Answer 1

I = A/s^2 + 8A/(600-s^2)
where I = illumination, s = distance from A, A is a constant
Take the derivative of I relative to s, set to zero, and solve for s, the distance