lim(Δx→0) [ƒ(x₀ + 2Δx) - ƒ(x₀)]/Δx = 1/2 lim(Δx→0) [ƒ(x₀ + 2Δx) - ƒ(x₀)]/(2Δx) · 2 = 1/2 ƒ'(x₀) · 2 = 1/2 ƒ'(x₀) = 1/4 ƒ'(x) = lim(Δx→0) [ƒ(x + Δx) - ƒ(x)]/Δx
