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Solve the following equation: cos4theta=...

Solve the following equation: `cos4theta=cos2theta`

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Given,`cos4theta=cos2theta`
=`cos4theta-cos2theta`
=`-2sin((4theta+2theta)/2).sin((4theta-2theta)/2)`
=`sin3thetasintheta=0`
`theta=0` or `theta=npi`
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