Free Grade 3 Introduction to Introducing Angle Bisector Common Errors Lesson Plans
Free Grade 3 lesson plans for Introduction to Introducing Angle Bisector Common Errors: 12 real questions with a full answer key and worked solutions. Angles on a straight line add to 180°, around a point to 360°, and inside a triangle to 180°. A polygon with n sides has interior angles adding to (n − 2) × 180°.
Free
Core
15 min
24
Learning objectives
Every objective is checkable, and each one maps to an activity and an assessment.
- UnderstandExplain introduction to introducing angle bisector common errors
Explain introduction to introducing angle bisector common errors accurately in a familiar context.
Assessed by: Exit ticket of four short items
- ApplyCalculate introduction to introducing angle bisector common errors
Calculate introduction to introducing angle bisector common errors accurately in a familiar context.
Assessed by: Exit ticket of four short items
- AnalyseCompare introduction to introducing angle bisector common errors
Compare introduction to introducing angle bisector common errors accurately in a familiar context.
Assessed by: Exit ticket of four short items
- EvaluateJustify introduction to introducing angle bisector common errors
Justify introduction to introducing angle bisector common errors accurately in a familiar context.
Assessed by: Exit ticket of four short items
Prerequisites
Close these gaps first — each has its own free lesson, worksheet and quiz.
How Introduction to Introducing Angle Bisector Common Errors works
Angles on a straight line add to 180°, around a point to 360°, and inside a triangle to 180°. A polygon with n sides has interior angles adding to (n − 2) × 180°.
12 practice questions
Easy to hard, 24 marks in total. Try them first, then open the answers.
- 1.Two angles on a straight line. One is 134°. Find the other.[1]
- 2.Two angles on a straight line. One is 72°. Find the other.[1]
- 3.Two angles on a straight line. One is 136°. Find the other.[1]
- 4.Two angles on a straight line. One is 82°. Find the other.[1]
- 5.A triangle has angles 70° and 32°. Find the third angle.[2]
- 6.A triangle has angles 82° and 37°. Find the third angle.[2]
- 7.A triangle has angles 20° and 109°. Find the third angle.[2]
- 8.A triangle has angles 45° and 44°. Find the third angle.[2]
- 9.Find the size of each interior angle of a regular 9-sided polygon.[3]
- 10.Find the size of each interior angle of a regular 5-sided polygon.[3]
- 11.Find the size of each interior angle of a regular 7-sided polygon.[3]
- 12.Find the size of each interior angle of a regular 10-sided polygon.[3]
Show answers and working
1. 46°
Angles on a straight line add to 180°. 180 − 134 = 46°.
2. 108°
Angles on a straight line add to 180°. 180 − 72 = 108°.
3. 44°
Angles on a straight line add to 180°. 180 − 136 = 44°.
4. 98°
Angles on a straight line add to 180°. 180 − 82 = 98°.
5. 78°
Angles in a triangle add to 180°. 180 − 70 − 32 = 78°.
6. 61°
Angles in a triangle add to 180°. 180 − 82 − 37 = 61°.
7. 51°
Angles in a triangle add to 180°. 180 − 20 − 109 = 51°.
8. 91°
Angles in a triangle add to 180°. 180 − 45 − 44 = 91°.
9. 140°
Sum of interior angles = (9 − 2) × 180 = 1260°. Each angle = 1260 ÷ 9 = 140°.
10. 108°
Sum of interior angles = (5 − 2) × 180 = 540°. Each angle = 540 ÷ 5 = 108°.
11. 128.57°
Sum of interior angles = (7 − 2) × 180 = 900°. Each angle = 900 ÷ 7 = 128.57°.
12. 144°
Sum of interior angles = (10 − 2) × 180 = 1440°. Each angle = 1440 ÷ 10 = 144°.
Worked examples
Two angles on a straight line. One is 74°. Find the other.
- Angles on a straight line add to 180°.
- 180 − 74 = 106°.
- Answer: 106°
A triangle has angles 39° and 96°. Find the third angle.
- Angles in a triangle add to 180°.
- 180 − 39 − 96 = 45°.
- Answer: 45°
Find the size of each interior angle of a regular 8-sided polygon.
- Sum of interior angles = (8 − 2) × 180 = 1080°.
- Each angle = 1080 ÷ 8 = 135°.
- Answer: 135°
Interactive practice
Free, no account required — answer on screen or print it.
Common mistakes
What learners typically get wrong, and how to fix it.
Reads the wrong scale on a protractor.
Correction: Start from the 0 on the arm you are measuring from.
Uses 360° for a triangle.
Correction: Triangle = 180°, quadrilateral = 360°.
Teacher tips
- · Estimate the angle type before measuring.
Parent tips
- · Spot right angles around the house.
Real-life applications
- · Ramps, clock hands, building and design.
Assessment objectives
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- Start with Introducing Angle Bisector Word Problems. Each one has its own free lesson, worksheet and quiz.
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