Greatest Angle in a Triangle

Our adopted textbook, Holt Geometry, has the following definitions:

"Acute triangle is a triangle with three acute angles."

"Obtuse triangle is a triangle with one obtuse angle."

"Right triangle is a triangle with one right angle."

Using the triangle sum theorem, one would see that there can only be one right angle or one obtuse angle in any triangle.

In my class, I don't see any problem if my students would come up with the following definitions:

Acute triangle is a triangle whose greatest angle is acute.

Obtuse triangle is a triangle whose greatest angle is obtuse.

Right triangle is a triangle whose greatest angle is right.


And what do you think of this take on equiangular triangle:

"Equiangular triangle is a triangle whose greatest angle is 60 degrees"?

A Classifying Triangles Activity

Here's an activity that I have been using to help my students achieve mastery on classifying triangles by side lengths and angle measures.

The primary objectives of this activity are (1) to master vocabulary, and (2) be able to correctly relate the different triangle classifications with each other.

The activity involves a 4 X 5 table. The top row will feature the triangle classifications based on angle measures: acute, right, obtuse, and equiangular. The left column will feature the triangle classifications based on side lengths: scalene, isosceles, and equilateral.

In this activity, the students, individually or in groups, will determine if triangles can fall under two such classifications. For example: Is it possible to draw a triangle that is both acute and scalene? If so, the students will draw that triangle and label it appropriately. If not, then they may write NP for not possible.

I find this activity great for reviewing vocabulary (scaffolding). It is also great for classroom talk and more questioning.

What I like the most about this activity is its "friendliness" to diverse learners, from the learning-challenged to the gifted, and from the color-blind to the most artistic.

This poster was created by Kendra Cobos, Edgar Devora,

Vincent Grimaldo and Rey de Leon in my Geometry class.

Freshmen Irma Mata, Alex Tenopala, Kaela Garcia and Amber

Hernandez created this poster in my Geometry class.

Poster created by Dalia Gutierrez, Victoria Gomez and Berenice Pacheco.