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Prove that Cos²A+cos²(A+B)-2cosA.cosB.cos(A+B)=sin²B

Prove that
Cos²A+cos²(A+B)-2cosA.cosB.cos(A+B)=sin²B

Grade:11

1 Answers

Parnav Bansal
46 Points
4 years ago
LHS,
Cos^2A +cos(A+B) [Cos(A+B) - 2cosA cosB ]
Cos^2A+cos(A+B) [ cosA cosB - sinA sin B -2 cosA cosB]
Cos^2A - cos (A+B) [ cos (A-B) ]
Cos^2A -( cos^2A -sin^2B)
Sin^2B = RHS
Hence proved
Cos

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