If cosα+cosβ+cosγ=0 = sinα+sinβ+sinγ, prove that
(i) cos3α+cos3β+cosγ = 3cos(a+β+γ)
(ii) sin3α+sin3β+sinγ = 3sin(α+β+γ)
(iii) cos2α+cos2β+cos2γ = 0
(iv) sin2α+sin2β+sin2γ = 0
(Hints: Take a=cis α, b=cis β, c=cis γ, a+b+c=0 ⇒ a^3 +b^3 +c^3 =3abc
(1/a)+(1/b)+(1/c)=0 ⇒ a^2 +b^2 +c^2 =0)
(v) cos^2 α+cos^2 β+cosγ = sin^2 α+sin^2 β+sin^2 γ = (3/2).
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