Download Section 5.1 Classifying Triangles

Geometry – Chapter 5 Lesson Plans
Section 5.1 –Classifying Triangles
Enduring Understandings: The student shall be able to:
1. identify the parts of triangles and to classify triangles by their parts
Warm up/Opener: Review/re-teach concepts and solutions via sample problems of
previous sections.
Standards:
11. Points, Lines and Planes
Classifies triangles as acute, right, obtuse, equilateral, isosceles, scalene; and
classifies polygons as regular, convex, congruent.
Essential Questions: How do we classify triangles?
Activities:
Lesson/Body:
A triangle is formed when three noncollinear points are connected by segments. Each
pair of segments forms an angle of the triangle. The vertex of each angle is a vertex of
the triangle.
Talk about the uniqueness of a triangle – the only rigid polygon. Show pictures of uses
of triangles from my pictures. Also include the “live hinge” and the physiology of a
dog’s hind leg – why can a dog run so much faster than a person?
The symbol for a triangle is , so ABC, is triangle ABC. How many other ways can we
identify ABC?
Classify triangles by angles: acute, obtuse, and right
Classify triangles by sides: scalene, isosceles, and equilateral.
NOTE: All equilateral triangles are also isosceles triangles.
Some parts of isosceles triangles have special names:
The congruent sides are called legs.
The angle formed by the congruent sides is called the vertex angle.
The side opposite the vertex angle is called the base.
The two angels formed by the base ane one of the congruent sides are called base angles.
Do the examples, especially example 3
Assessments:
Have students come to the board and draw various triangles.
Do the Check for Understanding.
CW WS 4.1 of the Red Book
HW pg 190-192, # 9 – 17 odd, 18-22 all, 27, 28 (12)
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.