# How do you solve 21x^2=12x by factoring?

Sep 28, 2015

First subtract $12 x$ on both sides

#### Explanation:

$\to 21 {x}^{2} - 12 x = 0$

You can write $21 = 3 \cdot 7$ and $12 = 3 \cdot 4$.
You can also factor out one $x$:

$\to 3 \cdot 7 \cdot x \cdot x - 3 \cdot 4 \cdot x = 0$
$\to 3 \cdot x \cdot \left(7 x - 4\right)$

So either $x = 0$
Or $7 x - 4 = 0 \to 7 x = 4 \to x = \frac{7}{4}$