Explains that the intersection of the three angle bisectors of a triangle form the incenter of the triangle. [7:58]

Proof that the area of a triangle is equal to half the inradius times the perimeter of the triangle, or the area is equal to the inradius times the semiperimeter. This video also appears in the Geometry: Circles strand. [7:29]

Provides a review of perpendicular bisectors, angle bisectors, medians, and altitudes and the special points of concurrency formed by these parts of a triangle.