Given: The coordinates of triangle PQR are P(0, 0), Q(2a, 0), and R(2b, 2c).
Prove: The line containing the midpoints of two sides of a triangle is parallel to the third side.

As part of the proof, find the midpoint of line QR.
(b, c)

(a − b, c)

(a + b, c)

(a, c)