Met de productregel
\eqalign{ & f(x) = \sqrt {2x^2 + x} \cr & f(x) = \sqrt {x(2x + 1)} \cr & f(x) = \sqrt x \cdot \sqrt {2x + 1} \cr & f'(x) = \frac{1} {{2\sqrt x }} \cdot \sqrt {2x + 1} + \sqrt x \cdot \frac{1} {{2\sqrt {2x + 1} }} \cdot 2 \cr & f'(x) = \frac{{\sqrt {2x + 1} }} {{2\sqrt x }} + \frac{{\sqrt x }} {{\sqrt {2x + 1} }} \cr & f'(x) = \frac{{\sqrt {2x + 1} }} {{2\sqrt x }} \cdot \frac{{\sqrt {2x + 1} }} {{\sqrt {2x + 1} }} + \frac{{\sqrt x }} {{\sqrt {2x + 1} }} \cdot \frac{{2\sqrt x }} {{2\sqrt x }} \cr & f'(x) = \frac{{2x + 1}} {{2\sqrt x \cdot \sqrt {2x + 1} }} + \frac{{2x}} {{2\sqrt x \sqrt {2x + 1} }} \cr & f'(x) = \frac{{4x + 1}} {{2\sqrt x \cdot \sqrt {2x + 1} }} \cr & f'(x) = \frac{{4x + 1}} {{2\sqrt {2x^2 + x} }} \cr}
Echt handig is het niet maar 't kan...:-)