# How do you factor 21x^3 - 28x?

Jul 5, 2016

$x = 0 \mathmr{and} x = \pm \frac{2 \sqrt{3}}{3}$

#### Explanation:

Start by taking out the common factor, 7x
$7 x \left(3 {x}^{2} - 4\right) = 0$
$7 x = 0 \mathmr{and} 3 {x}^{2} - 4 = 0$
$x = 0 \mathmr{and} {x}^{2} = \frac{4}{3}$
$x = 0 \mathmr{and} x = \pm \frac{2}{\sqrt{3}}$

$x = 0 \mathmr{and} x = \pm \frac{2 \sqrt{3}}{3}$