Download Section 5.2 Angles of a Triangle

Geometry – Chapter 5 Lesson Plans
Section 5.2 – Angles of a Triangle
Enduring Understandings: The student shall be able to:
1. use the angle sum theorem
Warm up/Opener:
Standards:
14. Points, Lines and Planes
States and applies the triangle sum, exterior angles, and polygon angle sum theorems.
Essential Questions: We have been told the sum of the interior angles of a triangle
equals 180 degrees. How can we prove it? How can we use that information?
Activities:
Lesson/Body:
Prove that the sum of the measures of the angles of a triangle is 180 via line through the
vertex and parallel to the base, using transversals and alternate interior angles.
Thm 5-1 Angle Sum Theorem: The sum of the measures of the angles of a triangle is 180.
A + B + C = 180 or x + y + z = 180
Thm 5-2: The acute angles of a right triangle are complementary
A + B = 90 or x + y = 90
An Equiangular Triangle is a triangle in which all three angles are congruent.
Equiangular triangles are equilateral, and visa versa.
Thm 5-3: The measure of each angle of an equiangular triangle is 60.
Show the measure of the exterior angle is the sum of the measures of the two remote
interior angles. This will be covered more in Section 7.2.
Assessments:
Do the Check for Understanding.
CW WS 4.2 of the Red Book
HW pg 196 – 197, # 9 – 29 odd (11)
Reflect on the lesson, the student’s response, and their understanding. Modify the
beginning of the next class to include review of weak understandings, and enforce
developing ideas.