Question

If `2 sin^(2) ((pi//2) cos^(2) x)=1-cos (pi sin 2x), x ne (2n + 1) pi//2, n in I`, then `cos 2x` is equal to
A. `1//5`
B. `3//5`
C. `4//5`
D. `1`

Answer 1

Correct Answer - B
The given equation is equivalent to
`2 sin^(2) ((pi//2) cos^(2) x)=2 sin^(2) ((pi//2) sin 2x)`
or `cos^(2) x= sin 2x`
or `cos x (cos x -2 sin x)=0`
`rArr 1-2 tan x=0` as `cos x ne0, x ne (2n+1) pi/2`
or `tan x=1/2`
`rArr cos 2x=(1-tan^(2) x)/(1+tan^(2) x)=3/5`