Question
Tue September 11, 2012 By:

# using formula cos2a=2cos2a-1 find the value of sin30 if cos 60=1/2

Tue September 11, 2012
cos2A = 2cos2A - 1
Put A = 30
cos60 = 2cos230 - 1
1/2 = 2cos230 - 1
2cos230 = 3/2
cos230 = 3/4
cos 30 = root 3/2
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