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.

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.

7. d. 64

8. i. 32

9. c. 125

10. j. none of the above

11. d. 81

12. i. 216

13. e. none of the above

14. g. 240

15. e. none of the above

16. g. 32

17.   e. none of the above