Answer
The origin can be used to test whether a linear equation is a direct variation function because if it is plugged into a linear equation and the equation becomes $0=0$, it is a direct variation.
Work Step by Step
A direct variation:
$y=\frac{7}{3}x$
$0=\frac{7}{3}(0)$
$0=0$
Not a direct variation:
$y=8x+6$
$0=8(0)+6$
$0=6$
