because the equation y=9x does not have a y-intercept (all slopes come in the form y=mx+b -- it can be written differently though) and since there is no 'b' that means the y-intercept is 0. So whenever there is no y-intercept, the slope starts at 0.
The angels across from each other are the same. That makes the sides and the interior lines the same as well. So that means the lines cannot cross each other. They are parallel
