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Let f(x) be a function defined on (-a,a)...

Let f(x) be a function defined on `(-a,a)` with a gt 0. Assume that f(x) is continuous at x = 0 and `lim_(xrarr0) (f(x)-f(kx))/(x)=alpha,` where `k in (0,1)` then

A

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

B

`f'(0^(-))=(alpha)/(1-k)`

C

f(x) is defferentiable at x = 0

D

f(x) is non-differentiable at x = 0

Text Solution

Verified by Experts

The correct Answer is:
B, C, D
`because" "underset(xrarr0)(lim)(f(x)-f(lalpha))/(x)=alpha`
`rArr" "underset(xrarr0)(lim)(f(x)-f(0)+f(0)-(kx))/(x)=alpha`
`rArr" "underset(xrarr0)(lim)((f(x)-f(0))/(x)-(f(lx)-f(0))/(x))=alpha`
`rArr" "(underset(xrarr0)(lim)(f(x)-f(0))/(x))-(underset(xrarr0)(lim)(f(kx)-f(0))/(kx))k=alpha`
`rArr" "{{:(underset(xrarr0^(-))(lim)(f(x)-f(0))/(x)-underset(xrarr0^(-))(lim)(f(kx)-f(0))/(kx)k=alpha),(underset(xrarr0^(+))(lim)(f(kx)-f(0))/(kx)-underset(xrarr0^(+))(lim)(f(kx)-f(0))/(kx).k=alpha):}`
`={{:(f'(0^(-))-kf'(0^(-))=alpha),(f'(0^(+))-kf'(0^(+))=alpha):}`
`={{:((1-k)f'(0^(-))=alpha),((1-k)f'(0^(+))=alpha):}`
`={{:(f'(0^(-))=(alpha)/(-k)),(f'(0^(+))=(alpha)/(1-k)):}`
`therefore" "f'(0)=f'(0^(-))=f'(0^(+))=(alpha)/(1-k)`
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