if alpha = 2π/7 , prove that cos alpha + cos 2 alpha + cos 4 alpha = -1/2 . Also deduce sin alpha + sin 2 alpha + sin 4 alpha = √7/2 .
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Complex Numbers And Quadratic Equations
If a= cos((2pi)/7)+isin((2pi)/7) , alpha= a+a^2+a^4,and beta =a^3+a^5+a^6 then alpha ,beta are the roots of the equation
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