Objective: Analyze and classify triangles based on side length, angle measure or both.
In Lesson 13, students are introduced to the precise definition of a triangle and further their understanding of right, acute, and obtuse angles by identifying them in triangles. They then classify triangles as right, acute, or obtuse based on angle measurements. Through a paper-folding activity with a right triangle, students see that the non-right angles of a right triangle are complementary. They also learn that triangles can be classified as equilateral, isosceles, or scalene based on side lengths. For isosceles triangles, lines of symmetry are identified, and a folding activity demonstrates that base angles are equal. Folding an equilateral triangle highlights multiple lines of symmetry and proves that not only are all sides equal in length, but also that all interior angles have the same measure.
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