To convert degrees to radians, simply multiply it with π/180 and express it in the simplest fraction and in terms of π. Conversely, to convert degrees to radians, multiply it with 180/π.
Here are the answers:
15. 13π/18
16. 4π
17. 7π/6
18. 1π/2
19. -1π/6
20. -3π/2
21. 60
22. 150
23. 120
24. 225
25. -135
26. -210
