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

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

$y=2x$y=2x i $\displaystyle y= \frac{1}{2} x$\displaystyle y= \frac{1}{2} x

$y=2$y=2 i $y=-2x$y=-2x