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Solve: cos3theta+costheta=0...

Solve: `cos3theta+costheta=0`

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`cos3theta+costheta=0`
`rArr cos3theta=-costheta=cos(pi-theta)`
`rArr 3theta=2npi+(pi-theta)` or `3theta=2npi-(pi-theta)`
`rArr 4theta=2npi+pi` or `2theta=2npi-pi`
`rArr 4theta=(2n+1)pi` or `2theta=(2n-1)pi`
`rArr theta =(2n+1)pi/4` or `theta=(2n-1)pi/2`. Ans.
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