Question 168985
Because the slopes are negative recipricals of each other then these lines are perpendicular.
y=x+7 (red line)
y=-x+2 (green line)
{{{ graph( 300, 300, -10, 5, -6, 10, x +7, -x +2) }}} (graph 300x300 pixels, x from -10 to 5, y from -6 to 10, of TWO functions x +7 and -x +2).