Question

How do you use a half angle formula to find the exact value of sin22.5 degrees?

Answer 1

Use the trig identity:
`2sin^2 a = 1 - cos 2a`. Trig table gives `cos 50 = (sqr2)/2`

`2.sin^2 (22,5) = 1 - (sqr2)/2 = (2 - sqr2)/2`
`sin^2 (22.5) = (2 - sqr2)/4`= 0.147

`sin 22.5 = 0.38`