Unit 3 Triangles Lesson 3 Introduction to Triangles

Unit 3 Triangles Lesson 3: Introduction to Triangles

Lesson 3: Introduction to Triangles Triangle: A polygon with 3 sides http: //www. geom. uiuc. edu/~wanous/concepttriangle. GIF

Vocabulary Sides: the segments that make the boundaries of the figure Vertices: The points where the sides come together Angles: formed by the joining of two sides of a polygon Exterior Angles: the angles outside the triangle that are supplementary to the corresponding interior angle D

Classifying Triangles by their angles Less than 90° Acute Triangle: all angles are _____ Greater than Obtuse Triangle: one angle is _____ 90° but less than 180° to 90° Right Triangle: one angle is Equal ______ to 60° Equiangular Triangle: all angles are Equal _______ equilateral *also an _____ triangle!

Classifying Triangles by their sides Scalene Triangle: no sides arecongruent _____ two Isosceles Triangle: at least _____ sides are congruent Equilateral Triangle: all sides are______ NOTE: An equilateral triangle is a special kind of isosceles triangle

Example Problems Ex 1: Find x, QR, RS, and QS if QRS is an equilateral triangle. R 4 x Q 2 x + 1 6 x – 1 S

Ex 2: Find x, JM, MN, and JN if JMN is an isosceles triangle. M 2 x – 5 J 3 x – 9 x– 2 N

Triangle Angle Sum The sum of the angles in a triangle add up to ________. The sum of the acute angles in a right triangle add up to ________.

Each angle in an equilateral triangle is the _________ and measures ________. The measure of an exterior angle is equal to the sum of its remote interior angles.

Your Turn:

Homework Unit 3 Lesson 3 Worksheet