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0:20 Naming the elements of a triangle 1:36 Construction of an isosceles triangle 5:23 Properties of an isosceles triangle 6:49 Checking the properties by mirroring about the axis of symmetry 7:53 Formulation of the base angle theorem 8:09 Summary After a general introduction to the naming of the vertices, sides and angles of a triangle, an isosceles triangle is constructed. After the detailed construction, angles are measured and the properties of isosceles triangles are determined based on the side lengths and angles. These properties are checked by mirroring about the axis of symmetry. Finally, the base angle theorem for isosceles triangles is explicitly formulated.