A student graphs three of the four vertices of square ABCD. Which point could be the fourth vertex of the square? A (0, 0) B (3, 0) C (3, 3)

In order for it to be a square, we see that it has to have a distance of 3 from the points B and C, since the distance between A and B is 3. A square is a parallelogram, so AD needs to be parallel to BC. Hence, since the vector BC is (0,3), we have that the vector AD is also (0,3). So, adding the coordinates of the vector to A, we get that D=(0,3).