How do you evaluate cos(2π/3)?

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How do you evaluate cos(2π/3)?

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Answer 1 · 2015-11-05T18:36:00

$- \frac{1}{2}$ $-1/2$

Explanation:

This is easy if you know basic angles with radians and the basic values of cosine.

$π = 180$ $pi = 180$ degrees
$2 π = 180 \cdot 2$ $2pi = 180 * 2$ degrees $= 360$ $= 360$ degrees
$\frac{2 π}{3} = \frac{360 d e g r e e s}{3} = 120$ $(2pi)/3 = (360 degrees)/3 = 120$ degrees

If you know the unit circle, you know that $cos (120)$ $cos(120)$ is the opposite of $cos (60)$ $cos(60)$ (both in degrees). This is because they are in different quadrants.

Since $cos (60) = \frac{1}{2}$ $cos(60) = 1/2$
$cos (120) = - \frac{1}{2}$ $cos(120) = -1/2$

PM me if you don't know how the unit circle works :-).
Hope this helped.

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How do you evaluate cos(2π/3)?

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