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Question Number 158391 by mr W last updated on 03/Nov/21
ifα,β,γaretheanglesofatriangle,findsin2α+sin2β+sin2γsinαsinβsinγ=?
Commented by MJS_new last updated on 03/Nov/21
4
Answered by puissant last updated on 03/Nov/21
sin2α+sin2β+sin2γsinαsinβsinγ=4sinαsinβsinγsinαsinβsinγ=4.
Answered by mr W last updated on 03/Nov/21
2π−2γ=2α+2β−sin2γ=sin2αcos2β+sin2βcos2α−sin2γ=sin2α(1−2sin2β)+sin2β(1−2sin2α)sin2α+sin2β+sin2γ=2sin2αsin2β+2sin2βsin2αsin2α+sin2β+sin2γ=4sinαsinβ(cosαsinβ+cosαsinα)sin2α+sin2β+sin2γ=4sinαsinβsin(α+β)sin2α+sin2β+sin2γ=4sinαsinβsinγ⇒sin2α+sin2β+sin2γsinαsinβsinγ=4
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