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Question: Evaluate cos 22.5° using half-angle formula.


A ) 24
B ) 2 -22
C ) 2 +22
D ) 12

Steps to derive

1 cos 22.5° = + 1 + cos45o2
 [cos(x2) = + 1 + cosx2.]

2 = 1+222
 [cos 45° = 22.]

3 = 2 +22



Hence the right answer is Option C

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