How do you solve $2 cos 2 x + 1 = 0$ $2cos2x + 1 = 0$ ?

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How do you solve $2 cos 2 x + 1 = 0$ $2cos2x + 1 = 0$ ?

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Answer 1 · 2015-10-27T04:37:06

Solve 2cos 2x + 1 = 0

Ans: $\pm \frac{π}{3}$ $+- pi/3$

Explanation:

2cos 2x = -1
$cos 2 x = - \frac{1}{2}$ $cos 2x = - 1/2$ --> $2 x = \pm \frac{2 π}{3}$ $2x = +- (2pi)/3$ --> $x = \pm \frac{π}{3}$ $x = +- pi/3$
Check by calculator.
$x = \frac{π}{3}$ $x = pi/3$ --> $2 x = (\frac{2 π}{3})$ $2x = ((2pi)/3)$ --> $cos 2 x = - \frac{1}{2}$ $cos 2x = - 1/2$ --> cos 2x + 1 = 0. OK

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How do you solve $2 cos 2 x + 1 = 0$ $2cos2x + 1 = 0$ ?

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