Medians, altitudes and midsegments.

Median

Segment whose end points are a vertex of the triangle and the midpoint of the opposite side.

Altitude

Perpendicular segment from a vertex to the opposites side.

Median Theorem

The midland of a triangle intersect at a point that is 2/3 of the distance from each vertex to the midpoint of the opposite side.

Altitude Theorem

The lines containing the altitudes of a triangle are concurrent.

Orthocenter

Point of concurrency of the altitudes

Centroid

Point of concurrency of the medians

Midsegment

A segment that connects the midpoint of two sides of a triangle.

Midsegment Theorem

The Midsegment is gonna be parallel to the base and half of it.