let-give-z-e-i-2pi-5-and-a-z-z-4-b-z-2-z-3-find-a-equation-wich-have-a-and-for-rootsthen-find-the-values-of-cos-2pi-5-sin-2pi-5-cos-4pi-5-sin-4pi-5-cos-

Question Number 28163 by abdo imad last updated on 21/Jan/18

l e t g i v e z = e^{i \frac{2 π}{5}} a n d a = z + z^{4}, b = z^{2} + z^{3}

f i n d a e q u a t i o n w i c h h a v e a a n d f o r r o o t s t h e n f i n d

t h e v a l u e s o f c o s (\frac{2 π}{5)}), s i n (\frac{2 π}{5}), c o s (\frac{4 π}{5}), s i n (\frac{4 π}{5}), c o s (\frac{π}{5}) .