 So section 4.6 is all about isosceles triangles. Now isosceles triangles, the word isosceles comes from the Greek root iso and skelos. Iso means same and skelos means legs. And so when we talk about isosceles triangles we mean the legs are the same. Just like these legs in this triangle would be considered the same. So now let's talk about some parts of isosceles triangles. First off the base of an isosceles triangle is the one side length that isn't congruent with the other ones. The two legs of course are the sides that are congruent to each other. So there's a leg and another leg. So the angles that are connected to the base are called the base angles. The side or the angle opposite the base is called the vertex angle. And vertex if you care that the plural of vertex is vertices not vertexes.