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prove that cosA +cosB+cosC=1+r/R....

prove that cosA +cosB+cosC=1+r/R.

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`cosA + cos B + cosC = 1 + 4 sin((A)/(2)) sin((B)/(2)) sin((C)/(2))`
`= 1 + ([4R sin (A//2) sin (B//2) sin(C//2)])/(R) = 1 + (r)/(R)`
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CENGAGE PUBLICATION-PROPERTIES AND SOLUTIONS OF TRIANGLE-Illustration
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