127
Comparing angles
Textbook: Part 4, lesson 127, pp. 60–62
GoalComparing angles: laying one on another; right, acute, obtuse and straight angles.
New words
angle · burchakvertex of an angle · burchak uchiacute angle · o‘tkir burchakobtuse angle · o‘tmas burchak
Explanation
To compare angles, lay one on the other: the vertices on one point and one side of each on one line. If the other sides also match, the angles are equal; if the other side of one angle stays inside the other angle, that angle is smaller. An angle smaller than a right angle is acute; larger (but smaller than a straight angle) is obtuse. An angle whose sides form a straight line is a straight angle.
Worked examples
At 3:00 the hands form a right angle and at 6:00 a straight angle. At 5:00 the angle is larger than at 3:00 and smaller than at 6:00, so it is obtuse.
At 1:00 the angle is smaller than a right angle, so it is acute.
Class activity
“Angle hunt”: make a right-angle template from paper (a notebook corner). Children compare angles around the room with it and decide whether each is acute, right or obtuse.
Practice
1
What kind of angle do the hour and minute hands make at 3:00?
a right angle
2
What kind of angle do the hands make at 6:00?
a straight angle
3
At 5:00 is the angle between the hands acute, right or obtuse?
obtuse
4
How many right angles does a square have?
4
5
Put the obtuse, acute and right angles in order from smallest to largest.
acute, right, obtuse