You can
put this solution on YOUR website!2y=8x+4
y=8x/2+4/2
y=4x+2 This line has a slope=4. (RED LINE)
y=-1/4x This line has a slope=-1/4. (GREEN LINE)
Thus these lines are perpendicular as the slopes are negative recipricals of each other (4 & -1/4).
Proof:

(graph 300x300 pixels, x from -6 to 6, y from -6 to 6, of TWO functions 4x +2 and -x/4).