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A function f: R rarr R" satisfies sin x ...

A function `f: R rarr R" satisfies sin x cos y "(f(2x+2y)-f(2x-2y))= cos x sin y (f(2x+2y)+f(2x-2y)).`" If "f'(0)=(1)/(2),` then

A

`f''(x)=f(x)=0`

B

`4f''(x)+f(x)=0`

C

`f''(x)+f(x)=0`

D

`4f''(x)-f(x)=0`

Text Solution

Verified by Experts

`"We have "(f(2x+2y))/(f(2x-2y))=(sin(x+y))/(sin (x-y))`
`"or "(f(alpha))/(sin""(alpha)/(2))=(f(beta))/(sin""(beta)/(2))=K`
`"or "f(x)=K sin""(x)/(2)`
`therefore" "f'(x)=(K)/(2)cos""(x)/(2)`
`"and "f''(x)=(-K)/(4)sin""(x)/(2)`
`"or "4f''(x)+f(x)=0`
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