1.

If `sin^6theta+cos^6theta+kcos^2(2theta)=1`, then `k` is

Answer» `sin^6theta=cos^6theta=(sin^2theta+cos^2theta)(sin^4theta+costheta-sin^2thetacostheta)=1`
`(sin^2theta+cos^2theta)^2-3sin^2thetacos^2theta)=1`
`=1-3sin^2thetacos^2theta`
`=1-3/4*sin^2(2theta)`
`=1/4+3/4cos^2 2theta`
`3cos^2 2theta+4kcos^2 2 theta=3`
`cos^2 2 theta(3+4k)=3`
`k=3/4+tan^2theta`
`cos^2 2theta*(3+3tan^2 2theta)=3`
option d is correct.


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