prove that
Asked by | 16th May, 2008, 08:09: AM
Expert Answer:
cosθ+cos2θ+cos3θ=1/4
2cos2θcosθ+cos2θ=1/4
cos2θ(2cosθ+1)=1/4
(2cos2θ-1)(2cosθ+1)=1/4
4cos3θ+2cos2θ-2cosθ-5/4 = 0
let cosθ = t
16t3+8t2-8t-5 = 0
The only real root of this equation is 0.74.
hence, cosθ = 0.74
hence, θ = cos-1(0.74)
Answered by | 16th Jul, 2008, 12:03: PM
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