$
\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...:-)