Question 157194
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( 300, 300, -6, 6, -6, 6, 4x +2, -x/4 ) }}} (graph 300x300 pixels, x from -6 to 6, y from -6 to 6, of TWO functions 4x +2 and -x/4).