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The corner term represents the product of two small changes, $\Delta f \Delta g$. Because the functions are differentiable, both $\Delta f$ and $\Delta g$ are of order $h$ (proportional to the input increment).

Conditions: Functions $f$ and $g$ are differentiable at the point.; The input increment $h$ approaches zero.; The geometric model assumes a rectangle with sides $f(x)$ and $g(x)$.

The corner term represents the product of two small changes, $\Delta f \Delta g$. Because the functions are differentiable, both $\Delta f$ and $\Delta g$ are of order $h$ (proportional to the input increment).

Conditions: Functions $f$ and $g$ are differentiable at the point.; The input increment $h$ approaches zero.; The geometric model assumes a rectangle with sides $f(x)$ and $g(x)$.