In some appropriate units, time ($t$) and position ($x$) relation of a moving particle is given by $t = x^2 + x$. The acceleration of the particle is:
$\dfrac{dt}{dx} = 2x+1\Rightarrow v = \dfrac{1}{2x+1}$. $a = v\dfrac{dv}{dx} = \dfrac{1}{2x+1}\cdot\left(-\dfrac{2}{(2x+1)^2}\right) = -\dfrac{2}{(2x+1)^3}$.