Posted by **Emily** on Monday, May 3, 2010 at 8:52pm.

Find the exact value of cos(x/2) if sin x = 3/4 and x is in quadrant II.

==> I got (4-7)/2. Is this correct?

- Math Analysis -
**Reiny**, Monday, May 3, 2010 at 9:24pm
I can't read your symbols, but

if sinx = 3/4 in II then

cos x = -√7/4

cosx = 2cos^2 (x/2) - 1

-√7/4 + 1 = 2cos^2 (x/2)

(4-√7)/8 = cos^2 (x/2)

cos x/2 = √[(4-√7)/8]

- Math Analysis -
**Emily**, Monday, May 3, 2010 at 9:27pm
Oops, yeah those were supposed to be radicals :) thanks so much!!!!

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