It is possible to work out the coordinates of a missing corner of a rectangle given the coordinates of the other three corners.

Example

Three of the corners of a rectangle are at (4, 2), (8, 2) and (4, 8).  

Find the coordinates of the fourth corner.

Answer

(4, 2) and (8, 2) are the base points because the y-coordinate is 2 compared to (4, 8).

The missing point must have its y-coordinate at 8 also.

(4, 2) and (8, 2) have x-coordinates which differ by 4, so the missing point must have its x-coordinate 4 more than (4,8).....i.e. 4 + 4 = 8.

The missing point has coordinates (8, 8).

Does that make sense?

Let's have a go at some questions then!