Question

The diagram shows rays of light from a point source, P, that reach a detector, D, along two paths. One path is a straight line, while the other is bent by reflection off a mirror. What is the value of b, correct to one decimal place? Assume that all the points in the diagram lie in the same plane.

Answer 1

This can solved using the cosine law which is:

c² = a² + b² - 2ab cos θ

Using the values given from the problem

6² = b² + b² - 2bb cos 112.62

And solving for b

36 = 2b² - 2b² cos 112.62

b = 3.6

The answer is the 3rd option.