1. 15°= 15π÷180 = π÷12
2. 40° = 40π÷180 = 2π÷9
3. 65°= 65π÷180 = 13π÷36
4. 21°= 21π÷180= 7π÷60
5. 81°= 81π÷180 = 9π÷20
