Investigate the relationship between an interval joining the midpoints of two sides of a triangle and the third side. Click and drag any of the blue points to change the size and orientation of the triangle ABC.

- Click the check-box for the interval joining the midpoints of AB and BC. What does the relationship between <BDE and <BAC tell you about the sides DE and AC? Does the ratio of the length of DE to AC change for differing positions of A, B and C?
- Examine the results for the intervals joining the midpoints of the other two sides. What is the relationship between an interval joining the midpoints of two sides of a triangle and the third side?