Question

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 .
NO SPAMMING .
Correct answer will be marked brainliest . ​

Answer 1

Answer:

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

Answer 2

Answer:

see the answer in the attachment please mark as brainlist