Question

已知cos3θ/cosθ=1/3,求sin3θ/sinθ的值？

Answer 1

cos3θ=4cos^3(θ)-3cosθ
cos3θ/链告枣cosθ=4cos^2(θ)-3=1/3
4cos^2(θ)=10/友液3
cos^2(θ)=5/6
1-sin^2(θ)=5/6
sin^2(θ)=1/6
sin3θ=3sinθ-4sin^3(θ)
sin3θ/sinθ=3-4sin^2(θ)=3-(4/6)=7/棚拆3,7,