It's all about triangle's secondary parts.

1. Secondary Parts of a Triangle

2. • Concurrent lines (segments or rays) are lines
that intersect in a single point.

3. • Median of a Triangle- segment whose
endpoints are a vertex of the triangle and the
midpoint of the opposite side.
• Angle bisector of a triangle- a segment which
bisects an angle of the triangle and whose
endpoints are a vertex and a point on the
opposite side
• Altitude of a triangle- a segment from the
vertex of the triangle perpendicular to the line
containing the opposite side.

4. • Perpendicular bisector of a side of a triangle- a
line whose points are equidistant from the
endpoints of the given side
• Incenter- the point of concurrency of the 3 angle
bisectors of the triangle
• Centroid- the point of concurrency of the 3
medians of the triangle
• Orthocenter- the point of concurrency of the 3
altitudes of the triangle.
• Circumcenter – the point of concurrency of the 3
perpendicular bisectors of the sides of the
triangle.