f(x) = 2·x^3 + x - 1
m = (f(x + h) - f(x)) / h
m = ((2·(x + h)^3 + (x + h) - 1) - (2·x^3 + x - 1)) / h
m = ((2·(x^3 + 3·h·x^2 + 3·h^2·x + h^3) + (x + h) - 1) - (2·x^3 + x - 1)) / h
m = (2·x^3 + 6·h·x^2 + 6·h^2·x + 2·h^3 + x + h - 1 - 2·x^3 - x + 1) / h
m = (6·h·x^2 + 6·h^2·x + 2·h^3 + h) / h
m = 6·x^2 + 6·h·x + 2·h^2 + 1
lim h --> 0
f'(x) = 6·x^2 + 1
f'(3) = 6·3^2 + 1 = 55