This video tells us the method to work with the coordinate plane in algebra. The first step tells us the method to determine the coordinates of a given point on the coordinate plane. For this, go parallel to the x axis from the given point and see where it intersects the y axis. This is the y coordinate. Again, go parallel to the y axis from the given point to the x axis. The point of its intersection with x axis is the x coordinate. Now we have the coordinates and we have to find the points on the coordinate plane. Following the reverse of the previous method, we go parallel to the x and y axis from the y and x coordinates respectively and find the point of their intersection. This is the required point. For the problem in the video, we plot the three points on the coordinate plane. We go parallel to the y axis and x axis from the first and third point. The point of their intersection is the fourth corner of the square. We find its coordinates by the method previously described. This finishes the task.