How do you solve $2costheta+1=0$ ?

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Answer 1 · 2018-07-12T09:15:24

The general solution of $2costheta+1=0$ is :

$theta=2kpi+-(2pi)/3 ,k in ZZ$

Here,

$2costheta+1=0$

$=>2costheta=-1$

$costheta=-1/2 < 0=>costheta=(pi-pi/3)=cos((2pi)/3)$

So,

$costheta=cos((2pi)/3)towhere, theta=arc cos(-1/2)=(2pi)/3$

$=>theta=2kpi+-(2pi)/3 ,k in ZZ$

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