Prove that: If 0<α,β,γ<π2, prove that sinα+sinβ+sinγ>sin(α+β+γ).
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Solution
Expansion of sin(α+β+γ) we have to prove that sinα(1−cosβcosγ)+sinβ(1−cosγcosα)+sinγ(1−cosαcosβ)+sinαsinβsinγ>0 Above is clearly true as 0<α,β,γ<π2 and each of 1−cosβcosγ is also +ive.