How do you use half angle formula to find sin112.5?

1 Answer
May 25, 2015

Use trig identity: 2sin^2 a = 1 - cos 2a

cos2(112,5)=cos225=cos(45+180)=cos45=22

2sin2112.5=1+22=2+22

sin2112.5=2+24=0.85

sin112.5=2+22

The negative answer is rejected because sin 112.5 is positive.

Check with calculator: sin 112.5 = 0.92 OK