Question 65625
m[(-3,1) to (0,3)] = (3 - 1)/(0 + 3) = 2/3
m[(-1,-2) to (2,0)] = (0 + 2)/(2 + 1) = 2/3
Opposite sides are parallel, so now we test the other sides.
m[(-3,1) to (-1,-2)] = (-2 - 1)/(-1 + 3) = -3/2
m[(0,3) to (2,0)] = (0 - 3)/(2 - 0) = -3/2
Opposite sides are parallel, so we have a parallelogram.
Rectangle?
m[(-3,1) to (-1,-2)] = (-2 - 1)/(-1 + 3) = -3/2
-m^(-1) or the perpendicular to the slope is 2/3
m[(-1,-2) to (2,0)] = (0 + 2)/(2 + 1) = 2/3
All four corners are perpendicular (forming ninety degree angles). This parallelogram is a rectangle.