Question

If you are given the coordinates of A, B, C, and D, how could you prove that ABCD is a rectangle?

A. Use the slope formula to show that AB∥CD, BC∥AD, AC⊥BD.
B. Use the distance formula to show that AB = CD, BC = AD, and AC = BD.
C. Use the distance formula to show that AB = CD, BC = AD, and use the midpoint formula to show that the midpoint of AC and the midpoint of BD are the same point.
D. Use the distance formula to show that AB = CD, and use the slope formula to show that AB∥CD and AB⊥BC.
E. Use the slope formula to show that AB∥CD, and use the distance formula to show that AB = CD and AC = BD.

Answer 1

• B. Use the distance formula to show that AB = CD, BC = AD, and AC = BD.
• D. Use the distance formula to show that AB = CD, and use the slope formula to show that AB∥CD and AB⊥BC.
• E. Use the slope formula to show that AB∥CD, and use the distance formula to show that AB = CD and AC = BD.

Explanation:

Your question does not say, "check all that apply," but I see three possible answers.

A -- can be ruled out because the diagonals of a rectangle are not necessarily perpendicular. This will show the figure is a rhombus.

B -- When both pairs of opposite sides are the same length, the figure is a parallelogram. A parallelogram with equal-length diagonals must be a rectangle.

C -- When opposite sides are the same length, the figure is a parallelogram. The diagonals of any parallelogram will have the same midpoint.

D -- When opposite sides are the same length and parallel, the figure is a parallelogram. A parallelogram with a right angle must be a rectangle.

E -- When opposite sides are the same length and parallel, the figure is a parallelogram. A parallelogram with equal-length diagonals must be a rectangle.

_____

Additional comment

My favorite method is to show AC = BD and their midpoints are the same. The midpoints of the diagonals being the same makes it a parallelogram, and the same-length diagonals makes the parallelogram a rectangle.