1.

`sin^(4)theta-cos^(4)theta` हैA. `cos2theta`B. `-sin2theta`C. `sin2theta`D. `-cos2theta`

Answer» Correct Answer - d
`sin^(4)theta-cos^(4)theta`
`(sin^(2)theta-cos^(2)theta)(sin^(2)theta-cos^(2)theta)`
`sin^(2)theta-cos^(2)theta(because sin^(2)theta+cos^(2)theta=1)`
`rArr-(cos^(2)theta=sin^(2)theta)=-cos2 theta`
`(because cos^(2)theta-sin^(2)theta=cos2theta)`


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