Triangle Classification: Analyzing Angles 53°, 117°, and 21°

Triangle Validity with Angle Sum Property

What kind of triangle is shown in the diagram below?

535353117117117212121AAABBBCCC

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:00 What triangle is given in the drawing
00:03 Let's start by checking if the triangle is indeed a triangle
00:06 The sum of angles in a triangle equals 180
00:09 Let's check if this holds true
00:23 We can see that the sum of angles is greater than 180, therefore it's not a triangle
00:27 And this is the solution to the question

Step-by-step written solution

Follow each step carefully to understand the complete solution
1

Understand the problem

What kind of triangle is shown in the diagram below?

535353117117117212121AAABBBCCC

2

Step-by-step solution

We calculate the sum of the angles of the triangle:

117+53+21=191 117+53+21=191

It seems that the sum of the angles of the triangle is not equal to 180°,

Therefore, the figure can not be a triangle and the drawing is incorrect.

3

Final Answer

The triangle is incorrect.

Key Points to Remember

Essential concepts to master this topic
  • Rule: Sum of all triangle angles must equal exactly 180°
  • Technique: Add given angles: 53° + 117° + 21° = 191°
  • Check: If sum ≠ 180°, the figure cannot be a valid triangle ✓

Common Mistakes

Avoid these frequent errors
  • Assuming any three-sided figure is automatically a triangle
    Don't just look at the shape and call it a triangle = wrong classification! A three-sided figure is only valid if its angles sum to 180°. Always check the angle sum property first.

Practice Quiz

Test your knowledge with interactive questions

Find the measure of the angle \( \alpha \)

949494AAABBBCCC92

FAQ

Everything you need to know about this question

Why can't a triangle have angles that add up to more than 180°?

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The angle sum property is a fundamental rule of geometry. In flat (Euclidean) geometry, the three interior angles of any triangle must always equal exactly 180° 180° . This is mathematically proven and cannot be violated.

What if the diagram looks like a triangle but the angles don't add to 180°?

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Then the diagram is incorrect or impossible! The drawing might be misleading, but mathematics doesn't lie. Trust the calculations over what you see - if angles sum to 191° 191° , it cannot be a real triangle.

Could there be a measurement error in the angles?

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That's possible in real-world situations, but in math problems, we work with the given values. Since 53°+117°+21°=191° 53° + 117° + 21° = 191° , we must conclude the figure is not a valid triangle.

What should I do when I get an angle sum that's not 180°?

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Always check your arithmetic first! If the sum is still not 180° 180° after double-checking, then the figure is not a valid triangle. State this clearly in your answer.

Are there different types of triangles I should know about?

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Yes! Acute triangles (all angles < 90°), right triangles (one angle = 90°), and obtuse triangles (one angle > 90°). But ALL valid triangles must have angles that sum to exactly 180° 180° .

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