Question

show that cos²a + cos² (a+ b) - 2cos a cos b cos (a+ b) = sin²b​

Answer 1

Step-by-step explanation:

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