SOLUTION: find the exact value of cos 195 degrees + cos 105 degrees

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Question 594726: find the exact value of cos 195 degrees + cos 105 degrees
Answer by lwsshak3(11628) About Me  (Show Source):
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find the exact value of cos 195 degrees + cos 105 degrees
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Sum to product formula:
cos s + cos t=2cos(s+t)/2*cos(s-t)/2
..
cos 195+cos 105=2cos(195+105)/2*(cos)195-95)/2
=2cos(300/2)*cos(90/2)
=2cos(150)*cos(45)
=2*-√3/2*√2/2
=-√6/2 ≈-1.224