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cos^(2)A+cos^(2)B-cos^(2)C=1-2sinA sinB ...

`cos^(2)A+cos^(2)B-cos^(2)C=1-2sinA sinB cosC`

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If A+B+C=pi , prove that : cos2A+cos2B-cos2C=1-4sinA sinB cosC

If A + B + C =180^@ , prove that : cos^2 A+ cos^2 B+cos^2 C=1-2 cos A cos B cosC .

If A+B+C=180^@ , then prove that cos^2 A + cos^2 B +cos^2 C=1-2cosA cosB cosC .

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If A+B+C= pi/2 , show that : cos^2 A + cos^2 B + cos^2 C = 2 + 2 sinA sinB sinC .

In DeltaABC , prove that: sin^(2)A+sin^(2)B+sin^(2)C =1-cos^(2)A+sin^(2)B+1-cos^(2)C =2-cos(A+B)cos(A-B)-cos^(2)C =2-cos(180^(@)-C)cos(A-B)-cosC.coc{180^(@)-(A+B)} =2+cosC.cos(A-B)+cos(A+B)] =2+cosC.2cosAcosB =RHS Hence proved.

If A+B+C=180^0 , prove that : cos^2 A + cos^2 B + cos^2 C + 2cosA cosB cosC=1 .