Suppose the minimum value of \(\displaystyle{{\cos}^{{2}}\theta}{\left(\theta_{{1}}-\theta_{{2}}\right)}+{{\cos}^{{2}}{\left(\theta_{{2}}-\theta_{{3}}\right)}}+{{\cos}^{{2}}{\left(\theta_{{3}}-\theta_{{1}}\right)}}\) is

Asher Olsen

Asher Olsen

Answered question

2022-04-02

Suppose the minimum value of cos2θ(θ1θ2)+cos2(θ2θ3)+cos2(θ3θ1) is 34

Answer & Explanation

Ashton Conrad

Ashton Conrad

Beginner2022-04-03Added 11 answers

As sin2x=2sinxcosx
cosθ1sinθ1+cosθ2sinθ2+cosθ3sinθ3=0
sin2θ1+sin2θ2+sin2θ3=0
sin2θ1+sin2θ2=sin2θ3 (1)
As cos2x=cos2xsin2x
cos2θ1+cos2θ2+cos2θ3=32=sin2θ1+sin2θ2+sin2θ3
scos2θ1+cos2θ2+cos2θ3=0
cos2θ1+cos2θ1=cos2θ3 (2)
Squaring and adding (1), (2)
sin22θ1+sin22θ2θ+2sin2θ1+sin2θ2+(cos22θ1+cos22θ2+2cos2θ1cos2θ2)=sin22θ3+cos22θ3
2+2cos2(θ1+θ2)=1
Using cos2x=2cos2x1
2+2(2cos2(θ1θ2)1)=1cos2(θ1θ2)=14
Similarly, θ2θ3, θ3θ1

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