I understand if two equations have the same slope they are parallel but what if they are the same number but?

one is a negative: for example y= -8x + 9 and y = 8x + 9. I don't believe that these lines would be parallel or perpendicular. It would take the shape of a greater than sign on a graph right?
Sorry if my question seems silly but I just need a little clarification. Thanks in advance

If you graph both lines and one makes an angle of theta with the x-axis, then the other makes an angle of (180 - theta) with the x-axis, (the angle in standard position)

That is, the angles at the x-intercepts are supplementary