How can the coordinates of two points on a line tell you if the line is horizontal or vertical?

A horizontal line is one the goes left-to-right, parallelto the x-axis of the coordinate plane. All points on the line will have the same y-coordinate. In the figure above, drag either point and note that the line is horizontal when they both have the same y-coordinate. A horizontal line has a slopeof zero

Step-by-step explanation:

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check above link.

graphically?   well, you graph them both, the solutions is where they both intersect each other, since there are two solutions, meaning they will meet twice, or namely the linear will run into the quadratic curve twice, and where they meet, those x,y coordinates are the solutions to the system.