# How do you solve abs(-3r)=9?

Apr 12, 2018

$r = 3$

#### Explanation:

Those bars around the $- 3 r$ are called absolute value bars and they turn everything inside positive, after they are in base form that is:
Ex: $| 3 - 10 | = x$ ; $| - 7 | = x$; $x = 7$
For this problem the $- 3 r$ is going to get turned positive:
$| - 3 r | = 9$ ; $3 r = 9$
Than divide the $3$:
$r = 3$

Apr 12, 2018

$r = - 3 , 3$

#### Explanation:

When you have an absolute value like this, you can set $- 3 r = 9$ and $- 3 r = - 9$.

Solve both equations by dividing both sides by -3 and get $r = - 3 , 3$.

If you want to check, try plugging -3 and 3 back into the original equation $\left\mid - 3 r \right\mid = 9$.
It works out: $\left\mid - 3 \left(- 3\right) \right\mid = 9$ and $\left\mid - 3 \left(3\right) \right\mid = 9$.