How do you differentiate ((5x+1)^2)(2x-1)?

$f ' \left(x\right) = {\left(5 x + 1\right)}^{2} \setminus \cdot 2 + 2 \left(5 x + 1\right) \setminus \cdot 5 \setminus \cdot \left(2 x - 1\right)$.
$f ' \left(x\right) = 2 \left(5 x + 1\right) \left(5 x + 1 + 10 x - 5\right) = 2 \left(5 x + 1\right) \left(15 x - 4\right)$
That way, you can quickly see the critical points of $f \left(x\right)$ are $x = - \setminus \frac{1}{5}$ and $x = \setminus \frac{4}{15}$.