If A+B+C = 180 degree then prove that sin2A + sin2B+ sin2C=2 +2 cosA cosB cosC .

If A+B+C = 180 degree then prove that $\sin^{2} A + \sin^{2} B + \sin^{2} C = 2 + 2 co s A c o s B co s C$ .

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