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Find the general value of theta from the...

Find the general value of `theta` from the equation `costheta+cos2theta + cos3theta=0`.

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`costheta+cos2theta+cos3theta=0`
`rArr cos3theta+costheta+cos2theta=0`
`rArr cos2theta(2costheta+1)=0`
`rArr cos2theta=0` or `2costheta+1=0`
Now, `cos2theta=0`
`rArr 2theta=(2n+1)pi/2`.
`=cos(pi-pi/3)=cos(2pi)/(3)`
`rArr theta=2npi+-(2pi)/(3)`. Ans.
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