Solve the following equation: `costheta+cos2theta+cos3theta=0`

Explanation

Combining costheta and cos3theta.

`(costheta+cos3theta)+cos2theta=0`

`2cos2thetacostheta+cos2theta=0`

or `cos2theta(2costheta+1)=0`

∴`cos2theta=0=cos(π/2),`

∴`2theta=(n+1/2​)π`

or `theta=(2n+1)π/4`

`2costheta+1=0`

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