Triangles
Classify triangles and explain their angles and special properties.
Meaning
A triangle is enclosed by three segments. It can be classified by side lengths or angles; a plane triangle's interior angles sum to 180 degrees. Draw through one vertex a line parallel to the opposite side. Alternate-angle relationships place copies of the other two interior angles at that vertex. The three angles form a straight angle, totaling 180 degrees.
Example
Practice for this concept
Scope and references
Topics
Classification by sides and angles, interior and exterior angles, isosceles and equilateral properties
Learning goal
Classify triangles and explain their angles and special properties.
Helpful background
Explore sides, angles, and parallel-line angle relationships as needed.
Triangles
These choice exercises use stated geometric conditions. They do not establish construction, drawing, spatial manipulation, written proof, or mastery of the whole geometry area.