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IfA+B+C=180°than prove that cosA+cosB-cosC=4cosA/2.sinB/2.cisC/2
Answers
Answered by
oobleck
use your sum-to product formulas.
cosA + cosB = 2 cos(A+B)/2 cos(A-B)/2
A+B = 180-C so cos(A+B)/2 = cos(90 - C/2) = sin C/2
and now you see how to finish it off.
cosA + cosB = 2 cos(A+B)/2 cos(A-B)/2
A+B = 180-C so cos(A+B)/2 = cos(90 - C/2) = sin C/2
and now you see how to finish it off.
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