Find the missing vertex that makes a rectangle {ACT}

If the points (3,1), (3,-1), and (-2,-1) are 3 vertices of a rectangle in the standard (x,y) coordinate plane, what is the fourth vertex?
A.)  (2,1)
B.)  (1,3)
C.)  (-1,-2)
D.)  (-2,1)
E.)  (-3,1)

Notice, in the first two points (3,1) and (3,-1), the x-coordinates are the same, and in the points (3,-1) and (-2,-1) the y-coordinates are the same  For the fourth point, to make a rectangle, you need to have matching y-coordinates with the point (3,1). Sounds confusing, therefore it's best to graph the given points:

(-2,1) would be the coordinates of the missing point.

D.)



- Algebra House