In the distance formula for square root of (x • 2 - x • 1)² + ( y • 2 - y • 1)² How would I tell what numbers go where? for example, (4, -9) and (5, 6)?
the points are (x1,y1) and (x2,y2)
surely your text had examples of this application.
Try plotting the points. You can draw a right triangle with the line between the points as the hypotenuse.