Looks like you are starting the concept of a derivative and are finding it by First Principles
f(0) = 0
f(0+.001) = .003999
so the slope of the secant
= (.00399 - 0)/(.001 - 0)
= 3.999
as you make your value of h get closer to zero, the slope of the secant will approach the slope of the tangent (the derivative) and it will get closer and closer to 4.
find the numerical deriviative of the given function at the indicated point. use h=0.001. is the function differentiable at the indicated point?
4x- x^2, x=0
1 answer