Use the half-angle identity to evaluate the given expression exactly.?

Matthew Ch

New member
(Enter the exact answer as a fraction. Decimal answers will not be accepted. Your answer should not contain sin, cos, or tan.)
How do i get the correct answer in Radical form..
a) Cos(7pi/8) - i got sqrt(1+sqrt(2)) /2
b) sin(7pi/8) - i got neg. - sqrt 2 -sqrt 2) / 2

Both of my answers were wrong, and Show Work as i can repeat later as i go over it?
Thanks Everyone.
 
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