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 Acute Triangle: all angles are _________ Obtuse Triangle: one angle is _________ Right Triangle: one angle is ___________ Equiangular Triangle: all angles are _____________ *also an _________ triangle! Less than 90° Greater than 90° but less than 180° Equal to 90° Equal to 60° equilateral

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

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

Ex 2: Find x, JM, MN, and JN if JMN is an isosceles triangle.

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.

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Homework Unit 3 Lesson 3 Worksheet