Google Classroom
GeoGebraGeoGebra Classroom

Heron's Formula for Area, then used to find inradius

Heron's Formula, explained at can be used to find the area of any triangle. Slice the triangle into 3 smaller triangles by connecting each vertex to the incenter, and you can see a relationship between the inradius and the area and perimeter of the triangle. A problem like this appeared on the AHSME in 1950: Here are some problems for practicing this. It is not asked, but you should also be able to find each altitude of the triangle once you can find its area.