f(x)is a function differentiable at x=1 and f'(1)=1/8.
what is the value of f(x)-f(1)
f'(x) denotes the derivative of f(x)
For x near 1, you can use linearlization, which is
f(x)=f'(1)(x-1)+f(1)
=(1/8)x+f(1)
Therefore, within the errors of the linearization,
f(x)-f(1) = (x-1)/8 (approximately)