1.

If `t a n^2theta=2t a n^2varphi+1`, prove that `cos2theta+s in^2varphi=0.`A. `-1`B. 0C. 1D. none of these.

Answer» Correct Answer - B
`tan^(2)theta=2tan^(2)phi+1`
or `1+tan^(2)theta=2(1+tan^(2)phi)`
`rArr sec^(2)theta=2sec^(2)phi`
`rArr cos^(2)phi=2cos^(2)phi=1=+cos2theta`
`rArr cos 2theta=cos^(2)phi-1=-sin^(2)phi`
`rArr sin^(2)phi+cos2theta=0`


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