Question

cos 3 theta = 4 cos³ theta - 3 cos theta​

Answer 1

cos3θ=cos(2θ+θ)

=cos2θcosθ−sin2θsinθ

=(cos2θ−sin2θ)cosθ−2sinθcosθsinθ

=cos3θ−sin2cosθ−2sin2θcosθ

=cosθ(cos2θ−sin2θ−2sin2θ)

=cosθ(cos2θ−3sin2θ)

=cos3θ−3sin2θcosθ

=cos3θ−3(1−cos2θ)cosθ

=cos3θ−3cosθ+3cos3θ

=4cos3θ−3cosθ

Thnx

Answer 2

Answer:

sorry

Step-by-step explanation:

cos3θ=cos(2θ+θ). =cos2θcosθ−sin2θsinθ. =(cos2θ−sin2θ)cosθ−2sinθcosθsinθ. =cos3θ−sin2cosθ−2sin2θcosθ.