# Different Types of Angles

Lesson Planning of Right, Acute and Obtuse Angles

Subject Mathematics

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;
1. Straight up,
2. Bend down,
3. 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 Movement of arm along with elbow reinforce acute and obtuse along straight line. Repeat to explain the difference from right angle. Let them use their arms and legs to make angles by bending and moving. (collect of sketch physical exercise pictures if possible) Make the angles with toothpicks, glue them on the paper, and label them. Find five objects in your home that have right angles in them. Draw some angles on the board and ask them to mark the angles as acute, right, obtuse, or straight (whole class activity). Recall the concept of horizontal and vertical lines and introduce the angle between them as right angle by asking does it make L shape? Assign pair work of labeling angles (questions can be assigned from book or prepare a worksheet). Invite one or two students to recap the points discussed today. Collect students work to check later.

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?

• 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: