SOLUTION: If cos A= 1/5, and angle A terminates in quadrant IV, find cos1/2 A

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Question 949212: If cos A= 1/5, and angle A terminates in quadrant IV, find cos1/2 A
Answer by lwsshak3(11628) About Me  (Show Source):
You can put this solution on YOUR website!
If cos A= 1/5, and angle A terminates in quadrant IV, find cos1/2 A
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half-angle formula:+cos%28x%2F2%29=sqrt%28%281%2Bcosx%29%2F2%29
+cos%28A%2F2%29=-sqrt%28%281%2B%281%2F5%29%29%2F2%29=-sqrt%28%286%2F5%29%2F2%29=-√(6/10)=-√(3/5)
check:
cosA=1/5 (Q4)
A≈281.54˚
A/2≈140.77˚
cos(A/2)=cos(140.77)≈-0.7746
exact value as computed=-√3/5≈-0.7746