1. centroid, the intersection of the medians of a triangle.

2. orthocenter, the intersection of the altitudes of a triangle.

3. circumcenter, the intersection of the perpindicular bisectors of the sides of a triangle.

4. circumcircle, the circle that is centered at the circumcenter and goes through the three vertices of the triangle.

5. incenter, the intersection of the angle bisectors of a triangle.

6. incircle, the circle that is centered at the incenter and is tangent to the three sides of the triangle.

7. nine-pt. circle center, center of the nine-point circle.

8. nine-pt. circle, passes through the three mid-points of the sides, the three feel of the altitudes, and the three mid-points of the segments from the respective vertices to the orthocenter.

9. medial triangle, triangle DEF in which D, E and F are the midpoints of the sides of the triangle ABC

10. square

12. hexagon

13. orthocenter/midpoint triangle, a triangle formed by first finding the orthocenter, H, of the triangle ABC. Then find the midpoints (D, E and F) of the segments AH, BH and CH. triangle DEF is the orthocenter/midpoint triangle.