What is the value of 2cos(pi/(13))cos((9pi)/(13))+cos((3pi)/(13))+cos((5pi)/(13)) ?

The value of 2cos(pi/(13))cos((9pi)/(13))+cos((3pi)/(13))+cos((5pi)/(13)) is 0

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2cos(pi/(13))cos((9pi)/(13))+cos((3pi)/(13))+cos((5pi)/(13))

2 cos (\frac{π}{13}) cos (\frac{9 π}{13}) + cos (\frac{3 π}{13}) + cos (\frac{5 π}{13})

0

Solution steps

2 cos (\frac{π}{13}) cos (\frac{9 π}{13}) + cos (\frac{3 π}{13}) + cos (\frac{5 π}{13})

Refine to a decimal form

= 0

2 csc^{2} (\frac{3 π}{4})

0.876 sin (- 32. 1^{\circ})

6 (cos (\frac{4 π}{3}) + i sin (\frac{4 π}{3}))

221 cos (5 5^{\circ})

- (- 1)^{3} - cos (- 1)

What is the value of 2cos(pi/(13))cos((9pi)/(13))+cos((3pi)/(13))+cos((5pi)/(13)) ?
The value of 2cos(pi/(13))cos((9pi)/(13))+cos((3pi)/(13))+cos((5pi)/(13)) is 0