Sum = 180°: Error Analysis & Misconceptions
Mathematics
Year 9
14 questions
~28 mins
1 views0 downloads
About This Worksheet
A worksheet focusing on understanding and correcting misconceptions related to the angle sum in triangles, emphasizing error analysis and reasoning.
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Sum = 180°: Error Analysis & Misconceptions
Subject: MathematicsGrade: Year 9
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Untitled Worksheet
Grade Year 9
A
Fluency & Practice
Answer all questions. Show your working in the grid spaces provided.
1.
Calculate the missing angle in a triangle where two angles are 65° and 50°.
[2 marks]2.
In a triangle, one angle is 90° and another is 45°, what is the third angle?
[2 marks]3.
A triangle has angles measuring 30° and 70°. Find the third angle.
[2 marks]4.
Construct a triangle where two angles are 40° and 60°. What is the measure of the third angle?
[2 marks]B
Problem Solving & Reasoning
Answer all questions with explanations where required.
1.
A triangle has one angle measuring 110°. The other two angles are equal. Find their measures and explain why they are equal.
[4 marks]2.
A student claims that the angles in a triangle can sum to 200°. Identify and correct the mistake in this reasoning.
[3 marks]3.
Explain why the sum of interior angles in a triangle is always 180° using a straight line and parallel lines.
[4 marks]C
Real-world Applications
Solve these contextual problems.
1.
A carpenter is designing a triangular frame with angles of 50° and 60°. What is the measure of the third angle?
[2 marks]2.
In a city park, a triangular area has two angles measuring 40° and 85°. If the third angle is to be an acute angle, what is the maximum possible measure of this angle?
[3 marks]D
Challenge & Extension
Attempt these advanced questions.
1.
Construct a triangle where one angle is twice another angle, and the third angle makes the sum 180°. Find the angles and justify your construction.
[4 marks]2.
Prove that the sum of interior angles in any triangle is 180° using a triangle drawn on a flat surface.
[4 marks]E
Mixed Review & Error Analysis
Identify errors in the following statements and correct them.
1.
A student says, 'One of the angles in a triangle can be 200°.' Is this correct? Explain and correct the misconception.
[3 marks]2.
A triangle has angles measuring 90°, 60°, and 30°. Is this possible? Why or why not?
[2 marks]3.
Identify and fix the mistake in claiming that the angles of a triangle can be 90°, 90°, and 10°.
[3 marks]Quick Actions
What is Remix?
Create a new worksheet based on this one. Change the grade level, topic, number of questions, or difficulty - then generate a fresh version.
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Details
- Created
- 1/1/2026
- Updated
- 1/1/2026
- Type
- worksheet