not giving the proper answer

if Î± lies in the fourth quadrant and cosÎ±=3/7 find the values of sinÎ±/2 and cosÎ±/2 ?

1 Answers

106

Asish Mahapatra ·2009-11-07 01:30:39

@ is in [3pi/2,2pi]
So, @/2 is in [3pi/4,pi] i.e. in second quad. (cos is negative while sin is positive)

cos(@) = 3/7 = 2cos²(@/2)-1

=> cos²(@/2) = 10/14
=> cos(@/2) = -√5/7

sin(@/2) = 1-cos²(@/2) = √2/7

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