Is my approach right?
I think if it is differentiable at x = 1, then it is also continuous at x = 1.
Then...
Any idea would be appreciable.
This is what I think:
In general the definition of the derivative is:
lim_(h->0) (f(x+h)-f(x))/h = df(x)/dx
You have given a function which is differentiable at x=1 so:
lim_(h->0) (f(1+h)-f(1))/h = f'(1)
If you compare this with the given limit: f(1) = ...