Sum = 180°: Problem Solving & Reasoning

Mathematics
Grade 8
14 questions
~28 mins
1 views0 downloads

About This Worksheet

A worksheet focusing on the key property that the interior angles of a triangle sum to 180°, including practice, problem-solving, real-world applications, and extension questions.

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Sum = 180°: Problem Solving & Reasoning

Subject: MathematicsGrade: Grade 8
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Untitled Worksheet

Grade Grade 8
A

Practice Questions

Answer all questions. Show your working in the grid spaces provided.
1.
Calculate the third angle of a triangle if two angles measure 65° and 50°. Show your working.
[2 marks]
2.
In a triangle, one angle is 90° and another is 45°. What is the measure of the third angle?
[2 marks]
3.
Construct a triangle where one angle is 70°, another is 60°, and verify that the third angle makes the sum 180°.
[3 marks]
4.
If one exterior angle of a triangle measures 110°, what is the sum of the two non-adjacent interior angles?
[2 marks]
B

Targeted Practice & Reasoning

Answer all questions clearly showing reasoning and calculations where necessary.
1.
Two angles of a triangle are 85° and 55°. Explain why the third angle must be less than 40° and calculate its exact measure.
[4 marks]
2.
A triangle has an exterior angle of 120°. If one of its interior opposite angles is 50°, find the other two interior angles.
[3 marks]
3.
Explain why the angles of a triangle cannot sum to more than 180° using examples or reasoning.
[3 marks]
4.
Construct a triangle where one angle is 40°, another 70°, and the third using the sum rule. Confirm the total is 180°.
[3 marks]
C

Real-world Applications

Solve these word problems by applying the sum of angles in triangles.
1.
A surveyor measures an angle of 125° at the corner of a triangular plot of land. The adjacent interior angles are supplementary. Find the two interior angles at this corner.
[4 marks]
2.
In a bridge design, two angles inside a triangular support are 80° and 60°. What is the measure of the third angle, and why is this important for structural stability?
[4 marks]
D

Challenge & Extension

Attempt these more difficult questions involving multiple concepts and reasoning.
1.
Prove that if two angles in a triangle are equal, the third angle is also equal, assuming the sum is 180°. Provide a detailed explanation.
[5 marks]
2.
Given a triangle with angles measuring (x°, 2x°, 3x°), find the value of x.
[3 marks]
E

Mixed Review & Error Analysis

Answer these questions to review key concepts and identify common mistakes.
1.
A student states that the sum of angles in a triangle can be 200°. Identify the mistake and correct it.
[2 marks]
2.
If an angle in a triangle is incorrectly calculated as 190°, what does this indicate about the problem?
[2 marks]

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Details

Created
1/1/2026
Updated
1/1/2026
Type
worksheet