**Corollary to Theorem 2.3**:
(The midpoint formula) Let (*x*_{1}, *y*_{1}) and
(*x*_{2}, *y*_{2}) be two points. The midpoint
between them has coordinates

**Proof**: We will define the midpoint as the point on the line
between (*x*_{1}, *y*_{1}) and (*x*_{2},
*y*_{2}) whose distance from each point is half of the total
distance between them. By Theorems 2.1 and
2.2 such a point is obtained by letting *t* =
1/2 in Theorem 2.1. In that case, 1 - *t* =
1/2, and the result follows.