f(x) = x3 - x
m = (f(x + h) - f(x)) / h
m = (((x + h)3 - (x + h)) - (x3 - x)) / h
m = ((x3 + 3·h·x2 + 3·h2·x + h3 - x - h) - (x3 - x)) / h
m = (x3 + 3·h·x2 + 3·h2·x + h3 - x - h - x3 + x) / h
m = (3·h·x2 + 3·h2·x + h3 - h) / h
m = 3·x2 + 3·h·x + h2 - 1
Für lim h → 0
m = 3·x2 - 1