Lesson 12

The purpose of this lesson is for students to classify angles as acute, obtuse, and straight, and to identify and draw acute and obtuse angles.

In previous lessons, students learned to measure angles and draw angles of given measurements. They saw that a \(90^\circ\) angle is called a right angle and is formed by two perpendicular lines. Students are also familiar with some benchmark angle measurements.

In this lesson, students classify angles by their size and identify angles as acute or obtuse in a variety of contexts. Students also learn that a \(180^\circ\) is called a straight angle.

• Students need their angle cards from the previous lesson. 

Before this point, students have had experiences of sorting mathematical objects relative to some benchmarks. In this lesson, angles are categorized by their size and relative to two benchmarks: \(90^\circ\) and \(180^\circ\). How readily did students conceptualize angles this way? Which past experiences of classifying objects would help to make this idea more intuitive?