Lesson Planning of Right, Acute and Obtuse Angles
Subject Mathematics
Grade 4^{th}
Students` Learning Outcomes
 Recognize right angle through horizontal and vertical lines.
 Demonstrate acute and obtuse angles through right angle.
Information for Teachers
 Types of angles: Zero angle, Straight angle, Obtuse angle, Right angle, and Acute angle.
 Angles are classified according to their degree (size).
 An acute angle is greater than 0° and less than 90°.
 A right angle equals exactly 90°.
 Note that a right angle is marked on the diagram as a small square on the point “B”.
 An obtuse angle is greater than 90° and less than 180°.
 A straight angle equals exactly 180°.
Material / Resources
Writing board, chalk/marker, duster, toothpicks, glue, clock (paper made or original), textbook
Introduction
 Act and demonstrate by sitting in three directions: as;
 Straight up,
 Bend down,
 Stretch back and hence introduce right, acute and obtuse angles respectively.
 Draw figures on board and tell them that L is right, V is acute angle.
 Clock hands work well for playing with angles, 3 o`clock and 9 o` clock represent right angles between the hour and minute hand and 2 o`clock shows an acute angle, 4 o`clock shows an obtuse angle, 9 o`clock shows straight angle.
Development
Activity 1

Sum up / Conclusion
 Acute angle is between 0° and 90°.
 Obtuse angle is between 90° and 180°.
 Right angle is of 90°.
 Straight angle is of 180°.
Assessment
 78° is either acute or obtuse angle?
 137° is either acute or obtuse angle?
 The right angle is of ___________ degree.
 Can someone show me a right angle?
 Can someone show me an acute angle?
 Can someone show me an obtuse angle?
Follow up
 Open a door, measure angle from floor and write its type after 5 seconds.
 Ask each student one by one to make different angles shape by stretching their arms.
 Match the following angles with their names: