You can put this solution on YOUR website! Find the exact values using double angle formulas:
a) cos 112.5 degrees
b) tan 22.5 degrees
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I think you meant using half-angle formulas:
..
a) cos 112.5º= cos (225/2)º=-√[(1+cos 225º)/2)]
1+cos 225º=1-√2/2=(2-√2)/2
(1+cos 225º)/2)=(2-√2)/4
-√[(1+cos 225º)/2)]=-√(2-√2)/2
cos 112.5º=-√(2-√2)/2
..
b) tan22.5º=tan (45/2)º=(sin 45º)/(1+cos 45º)=√2/2/(1+√2/2)
tan 22.5º=√2/(2+√2)
(