Question 169998
SLOPE FOR M=(13-9)/(5-3)=4/2=2
Y=mX+b
9=3*2+b
9=6+b
b=9-6
b=3
Y=2X+3 (RED LINE-M) 
SLOPE FOR N=(-11+9)/(5-3)=-2/2=-1
-9=-1*3+b
-9-3+b
b=-9+3
b=-6
Y=-X-6 (GREEN LINE-N)
{{{ graph( 300, 200, -6, 5, -10, 10, 2x +3, -x -6) }}} (graph 300x200 pixels, x from -6 to 5, y from -10 to 10, of TWO functions 2x +3 and -x -6).