Geometry Section 5.4 Midsegment s. A midsegment of a triangle is the segment joining the midpoints of two sides of a triangle. Theorem 5 .9 Midsegment Theorem A midsegment of a triangle is parallel to the third side and half as long as the third side.
Example: Consider with vertices A(0, 0), B(6, 2) and C(4, 8). Find the length of the midsegment joining the midpoints of and . Secondly, write the equation of the line containing this midsegment.