Question

the midpoint of line segment CD is M(5,-1). If the coordinates of C are (7,8), what are the coordinates of D

Answer 1

The midpoint of a line is midway between each vertice, so however far away 5,-1 is from 7,8 that is how far away it must be from point D. I would recommend drawing it out. If you draw it out on a coordinate plane, you can simply go count the opposite amount that you did when going from the midpoint to point C. So since you go right 2 and up 9 to get to point C, go left 2 and down 9 to get point D.