1. a segment from a vertex perpendicular to the opposite side
2. the two angles that include the base of an isosceles triangle
3. the third, unequal side of an isosceles triangle
4. a point on the interior of a triangle in which the three medians of the triangle intersect
5. a segment from a vertex to the midpoint of the opposite side
6. a point in which the three altitudes of the triangle intersect. it is possible for the orthocenter to occur on the triangle, on the interior of the triangle or on the exterior of the triangle
7. the angle formed by the two equal sides of an isosceles triangle