Question

If three consecutive vertices of a parallelogram ABCD are A (1, -2), B (3, 6) and C (5, 10), find its fourth vertex D

Answer 1

Let A (1, -2), B (3, 6) and C (5, 10) be the three vertices of a parallelogram ABCD and the fourth vertex be D (a, b).

Join AC and BD intersecting at O

We know that the diagonals of a parallelogram bisect each other 

Therefore, O is the midpoint of AC as well as BD.