Δy / Δx ≈
Exact derivative f'(x):
Function: f(x) = 0.5x³ - x
Move 'h' close to 0 to see the approximation converge to the exact value.
Function: f(x,y) = sin(x) * cos(y)
Red: Slice y=const (∂f/∂x). Blue: Slice x=const (∂f/∂y).