To find if something is a parallelogram, they 1 set of line segments need to have the the slope. In this equation, Slope equals x1 + x2 divided by y1 + y2 (Or the other way around, x2 + x1 divided by y2 + y1)
For your other point, it could be (-4,5)
If this is confusing, please tell me! I'll try to better explain. It also helps to draw out a graph so you can plot the points.
