differentiate
Performs numerical differentiation at a point.
Syntax

differentiate(expr, var, x[, ε])

expr
is an expression in one variablevar

var
is the variable inexpr

x
is the point at which the derivative is computed 
ε
is the radius aboutx
used for numerical differentiation

Description
differentiate
computes a symmetric difference quotient for a real function of a real variable at a particular point in its domain:
differentiate(f(t), t, x, ε) = [f(t + ε) − f(t − ε)] / (2⋅ε).
If omitted, ε
is set to 10^−6.
Examples
differentiate(x^2, x, 1)
2
differentiate(e^x, x, 1)
2.71828182846
∫(differentiate(x^2, x, t), t, 0, 2)
4