Q5 of 29 Page 1

Prove that .

Put x = cos Ɵ, we get


L.H.S = 3cos-1(cosθ) = 3θ


As,


∴ R.H.S = cos-1(4(cos θ)3 - 3 cos θ)

we know that by formula:

cos3θ = 4cos3θ - 3cosθ



L.H.S = R.H.S


Hence, proved

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