Chapter 3 Lesson 3 Objective To classify triangles

Chapter 3 Lesson 3 Objective: To classify triangles and find the measures of their angles.

Theorem 3 -7: Triangle Angle-Sum Theorem The sum of the measures of the angles of a triangle is 180. B A C

Example 1: Applying the Triangle Angle-Sum Theorem Find 1 35° 65°

Example 2: Applying the Triangle Angle-Sum Theorem Find C A 48° 67° B

Example 3: Using Algebra Find the values of x, y and z. To find the value of x, use ∆ACD. Triangle Angle-Sum Theorem ° 21 39 ° A To find the value of y, look at DCA and BCA. What kind of angle do they make? Straight To find the value of z, use ∆ACB. D 65° Triangle Angle-Sum Theorem x° y ° C z° B

Example 4: In triangle ABC, ACB is a right angle, and CD AB. Find the values of a, b and c. To find c, you know that right angle. C c° Using Algebra 70° ACB is a a° To find the value of a, use ∆ACD. A D Triangle Angle-Sum Theorem To find the value of b, use ∆CDB. Triangle Angle-Sum Theorem b° B

Types of Triangles

Example 5: Classifying a Triangle Classify the triangle by the sides and the angles. At least two sides are congruent, so the triangle is isosceles. All the angles are acute, so the triangle is acute. Classify the triangle by its sides and its angles. The triangle is an acute isosceles triangle.

Assignment pg. 134 -137 #1 -23; 31 -33; 37 -40