Before starting this lesson you should be familiar with the following terms and concepts, which we will quickly review here.
Lines segments and angles can both be bisected. This means a line is made to intersect them such that they are divided intot two equal parts.
Two lines are perpendicular if the angle of their intersection is 90 degrees.
Two triangles are congruent if they have the same size. That is, if you can place on on top of the other such that they overlap perfectly.
The medians of a triangle are the three line segments that join the three vertices with the midpoints of the sides opposite them. E.g.
The three medians intersect at a point within the triangle called the centroid.
A perpendicular bisector of a triangle is a line that bisects one of the sides, intersecting it at 90 degrees.
The perpedicular bisectors intersect at a point called the circumcenter. The circumcenter may be located on the inside or the outside of the triangle.
A line that bisects one of the angles at the vertices of a triangle is an angle bisector of that triangle.
Unlike the circumcenter, the incenter is always found within the triangle.
An altitude of a triangle is a perpendicular line drawn from one of its sides to the vertex opposite it.
