# Is y/(xz) = -4 a direct variation, inverse variation, joint or neither?

Aug 4, 2015

This is an example of joint variation.

#### Explanation:

"Joint variation" means "direct variation, but with two or more variables".

All the variables are directly proportional, taken one at a time.

Your equation is $\frac{y}{x z} = - 4$.

We can rearrange this to $y = - 4 x z$.

In words, we would say,

$y$ varies directly as $x$ and $z$, and the constant of variation is $- 4$.