$\displaystyle y= \frac{1}{3}x+2$\displaystyle y= \frac{1}{3}x+2

$\displaystyle y=- \frac{1}{3}x+2$\displaystyle y=- \frac{1}{3}x+2

$y=3x+1$y=3x+1

$y=-3x+1$y=-3x+1