Show that the points A(-2, 6), B(5, 3), C(-1, -11) and D(-8, -8) are the vertices of a rectangle.

1 answer

easy with vectors, but they are not usually a tool used in analytic geometry.

slope of AB is -3/7
slope of CD is -3/7, so AB||CD
slope of BC is 7/3
slope of AD is 7/3, so BC||AD

since slopes are negative reciprocals, the pairs of sides are perpendicular

So, ABCD is a rectangle.