Explain that there is a one to one correspondence between two points $(x_1,x_2),\space(x_3,x_4)$ in the coordinate plane and one point $(x_1,x_2,x_3,x_4)$ in the 4 dimensional coordinate space.
This seems to be a question that just seems to be correct by intuition. How could I actually explain this? I was a confused when I saw this in my textbook, especially confused on the ways of "explaining" such things.