Question 68295
SLOPE=(Y2-Y1)/X2-X1)
(-4+4)/(0+9)
0/9 REPRESENTS A VERTICLE LINE PASSING THROUGH  Y=-4
Y=-4 IS THE FORMULA FOR THIS LINE.
{{{ graph( 300, 200, -6, 5, -10, 10, y = -4) }}} (graph 300x200 pixels, x from -6 to 5, y from -10 to 10, y = -4).