1. Defining Triangles During this lesson, you will define triangles and their parts.

2. TERMDEFINITIONILLUSTRATION Right Triangle Acute Triangle Obtuse Triangle Scalene Triangle Isosceles Triangle Equilateral Triangle Median of a Triangle of t Altitude of a Triangle ∆ w/ all angles measuring < 90 degrees ∆ w/ exactly one right (90 degree) angle ∆ w/ exactly one angle measuring > 90 ∆ w/ no sides equal in measure ∆ w/ at least 2sides equal in measure ∆ w/ all sides congruent Segment of a ∆ which connects the vertex of one angle w/ the mid- point of the opposite side Perpendicular segment in a ∆ from a vertex to its opposite side

3. Isosceles Triangle Parts vertex leg Base angles Base In an isosceles triangle, the angle between the two sides of equal length is called ________________________________. The side opposite the vertex angle is called the _________ of the isosceles triangle. The two sides of equal length are called the ____________. The two angles opposite the two sides of equal length are called the ____________ of the isosceles triangle.

4. Final Checks for Understanding 1. Triangles can be classified by ____________________________. 2. True or False. Explain. An equilateral triangle is isosceles. 3.Name (and describe) the ways in which we classify triangles by the lengths of their sides. 4.Name (and describe) the ways in which we classify triangles by the measures of their angles.