Complete the coordinate proof of the theorem. Given: A B C D is a square. Prove: The diagonals of A B C D are perpendicular. Art
: A square A B C D is graphed on a coordinate plane. The horizontal x-axis and vertical y-axis are solid. The vertex labeled as A lies on begin ordered pair 0 comma 0 end ordered pair. The vertex labeled as B lies on begin ordered pair a comma 0 end ordered pair. The vertices C and D are unlabeled. Diagonal A C and B D are drawn by dotted lines. Enter your answers in the boxes. The coordinates of square ABCD are A(0, 0) , B(a, 0) , C(, a), and D(0, ). The slope of AC⎯⎯⎯⎯⎯ , when simplified, is equal to . The slope of BD⎯⎯⎯⎯⎯, when simplified, is equal to −1 . The product of the slopes is equal to . Therefore, AC⎯⎯⎯⎯⎯ is perpendicular to BD⎯⎯⎯⎯⎯.
Since the square is on a quadrant plane and it is a square, the fact that the lines cross in the center and start and stop in the corners allows you to tell that they are perpendicular.