hugo is writing a coordinate proof to show that the midpoints of a quadrilateral are the vertices of a parallelogram. he starts by assigning coordinates to the vertices of quadrilateral rstv and labeling the midpoints of the sides of the quadrilateral as a, b, c, and d. quadrilateral r s t v in a coordinate plane with vertex r at 0 comma 0, vertex s in the first quadrant at 2 a comma 2b, vertex t also in the first quadrant at 2 c comma 2 d, and vertex v on the positive side of the x-axis at 2 c comma 0. point a is between points r and s, point b is between points s and t, point c is between points t and v, and point d is between points r and v. enter the answers, in simplified form, in the boxes to complete the proof. the coordinates of point a are ( , ). the coordinates of point b are ( , ). the coordinates of point c are (2c, d) . the coordinates of point d are (c, 0) . the slope of both ab and dc is . the slope of both ad and bc is −bc−a . because both pairs of opposite sides are parallel, quadrilateral abcd is a parallelogram.