E2.4 Identify angles and classify them as right, straight, acute, or obtuse.
Skill: Recognizing Angles
The rays that form an angle (namely, the “arms” of an angle) meet at a vertex. The size of an angle is not affected by the length of its arms.
Source: The Ontario Curriculum. Mathematics, Grades 1-8 Ontario Ministry of Education, 2020.
In Grade 4, students must recognize and classify angles, either right, straight, acute, or obtuse.
Skill: Classifying Angles
In Grade 1, students identify angles on two-dimensional shapes and three-dimensional objects. Students know the concept of a right angle and should have benchmarks for it (for example, the corners of a sheet of paper or the angles of a square). In Grade 4, students should build understanding of a right angle and develop benchmarks (for example, the corners of a sheet of paper or the angles of a square). This understanding of a right angle will support them in beginning to identify the geometric properties of rectangles (see expectation E1.1). Students can use their knowledge of the right angle and their benchmarks to compare and classify various types of angles. By comparing the right angle with other angles, they can determine whether the other angles are smaller (acute angles) or larger (obtuse angles). The student thus uses the fundamental concept of transitivity to classify angles.
Source: translated from L’@telier - Ressources pédagogiques en ligne (atelier.on.ca).
Knowledge: Right Angle
A right angle is a quarter turn, and it is sometimes called a “square angle” because all angles of a square (or rectangle) are right. If two lines meet at a right angle, the lines are perpendicular.
Source: The Ontario Curriculum. Mathematics, Grades 1-8 Ontario Ministry of Education, 2020.
Knowledge: Acute and Obtuse Angles
Angles can be compared by overlaying one angle on another and matching them. An angle (turn greater than 90°) is an obtuse angle. An angle (turn less than 90°) is an acute angle.
Source: The Ontario Curriculum. Mathematics, Grades 1-8 Ontario Ministry of Education, 2020.
Knowledge: Straight Angle
A straight angle is formed by two line segments with the same vertex and different instructions. A half-turn, where the arms of the angle create a straight line, is a straight angle.
Source: The Ontario Curriculum. Mathematics, Grades 1-8 Ontario Ministry of Education, 2020.