Given $cos (2 \frac{π}{5}) = \frac{\sqrt{5} - 1}{4}$ $cos(2pi/5) = (sqrt(5)-1)/4$ , what is cos(3pi/5)?

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Given $cos (2 \frac{π}{5}) = \frac{\sqrt{5} - 1}{4}$ $cos(2pi/5) = (sqrt(5)-1)/4$ , what is cos(3pi/5)?

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Answer 1 · 2016-03-10T17:09:13

$\frac{1 - \sqrt{5}}{4}$ $(1-sqrt(5))/4$

Explanation:

$cos (θ) = - cos (π - θ)$ $cos (theta)= -cos(pi-theta)$

therefore

$cos (3 \frac{π}{5}) = cos (π - 2 \frac{π}{5}) = - cos (2 \frac{π}{5})$ $cos(3pi/5)=cos (pi-2pi/5)=-cos(2pi/5)$

$= \frac{1 - \sqrt{5}}{4}$ $=(1-sqrt(5))/4$

Answer 2 · 2016-03-10T17:20:24

$= - \frac{\sqrt{5} - 1}{4}$ $=-(sqrt5-1)/4$

Explanation:

$cos (\frac{3 π}{5}) = cos (π - \frac{2 π}{5}) = - cos (\frac{2 π}{5}) = - \frac{\sqrt{5} - 1}{4}$ $cos( (3pi)/5)=cos (pi-(2pi)/5)=-cos( (2pi)/5)=-(sqrt5-1)/4$

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Given $cos (2 \frac{π}{5}) = \frac{\sqrt{5} - 1}{4}$ $cos(2pi/5) = (sqrt(5)-1)/4$ , what is cos(3pi/5)?

2 Answers

Explanation:

Explanation:

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Given cos(2π5)=√5−14cos(2pi/5) = (sqrt(5)-1)/4, what is cos(3pi/5)?

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Given $cos (2 \frac{π}{5}) = \frac{\sqrt{5} - 1}{4}$ $cos(2pi/5) = (sqrt(5)-1)/4$ , what is cos(3pi/5)?