How do you find the exact value of $cos ((-2 pi) / 3)$ ?

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Answer 1 · 2018-07-03T09:16:25

$color(purple)(=> -1 / 2$

$cos -theta = cos theta$

$:. cos (-(2pi)/3) = cos ((2pi)/3)$

$cos ((2pi)/3) = cos (pi - (pi/3) = -cos (pi/3) = -1 / 2$

Answer 2 · 2018-07-03T09:25:56

$-1/2$

$cos(-(2pi)/3)=-cos(pi/3)=-1/2$

How do you find the exact value of cos ((-2 pi) / 3)cos ((-2 pi) / 3)?