we-have-z-e-2pi-7-i-a-z-z-2-z-4-and-b-z-3-z-5-z-6-we-know-a-b-1-and-1-b-a-find-S-cos-2pi-7-cos-4pi-7-cos-8pi-7-thanks-for-help-

Question Number 145162 by Skabetix last updated on 02/Jul/21

w e h a v e z = e^{\frac{2 p i}{7} i}

a = z + z^{2} + z^{4} a n d b = z^{3} + z^{5} + z^{6}

w e k n o w a + b = - 1 a n d 1 - b = a

f i n d S = c o s (\frac{2 p i}{7}) + c o s (\frac{4 p i}{7}) + c o s (\frac{8 p i}{7})

t h a n k s f o r h e l p

Commented by gsk2684 last updated on 03/Jul/21

statements in hypothesis are

cotradicts .

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