Right Triangle Analysis: Compare Angles ∢B and ∢A

Right Triangle Properties with Angle-Side Relationships

The triangle ABC is a right triangle.

Which angle is larger, B ∢B or A ∢A ?

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:00 Which angle is larger - A\B?
00:06 Right triangle according to the given
00:10 Sum of angles in a triangle equals 180
00:17 Let's substitute angle A
00:25 Let's isolate the sum of angles B+C
00:37 Sum of these angles equals 90
00:41 Therefore angle B must be less than 90
00:49 And this is the solution to the question

Step-by-step written solution

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1

Understand the problem

The triangle ABC is a right triangle.

Which angle is larger, B ∢B or A ∢A ?

AAABBBCCC

2

Step-by-step solution

In a right triangle ABC \triangle ABC , angle C ∢C is the right angle, which equals 90°. Therefore, the other two angles A ∢A and B ∢B must sum to 90°.

For any right triangle, if one acute angle is larger, the opposite side (leg) is longer. Conversely, if an angle is smaller, the opposing leg must be shorter.

Based on the triangle's diagram and fundamental right triangle properties, it appears that angle A ∢A is larger than angle B ∢B , given that larger angles oppose longer sides.

This conclusion follows from practical geometry, where angle recognition and placement determine relative size.

Therefore, we can conclude that A ∢A is greater than B ∢B , or A>B ∢A > ∢B .

3

Final Answer

A>B ∢A>∢B

Key Points to Remember

Essential concepts to master this topic
  • Rule: In right triangles, larger angles oppose longer sides
  • Technique: Compare side lengths BC vs AC to determine angle sizes
  • Check: Angles A + B + C = 90° + 90° = 180° total ✓

Common Mistakes

Avoid these frequent errors
  • Assuming angles are equal without measuring sides
    Don't assume ∠A = ∠B just because both are acute angles = wrong comparison! This ignores the angle-side relationship principle. Always compare the opposite sides first to determine which angle is larger.

Practice Quiz

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Is DE side in one of the triangles?
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FAQ

Everything you need to know about this question

How can I tell which angle is bigger without measuring?

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Look at the sides opposite each angle! In triangle ABC, angle A is opposite side BC, and angle B is opposite side AC. The longer side means the larger angle.

Why can't both acute angles be equal in a right triangle?

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They could be equal, but only in a special case called a 45-45-90 triangle where the two legs are equal length. In most right triangles, the legs have different lengths.

What's the relationship between angles and sides?

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This is a fundamental rule: larger angles are always opposite longer sides, and smaller angles are opposite shorter sides. This works in any triangle!

How do I identify which side is opposite which angle?

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The side opposite an angle is the side that doesn't touch that angle's vertex. For example, side BC is opposite angle A because it connects points B and C, not point A.

Can I solve this without the diagram?

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The diagram is crucial here! It shows the relative positions and lengths of the sides. Without visual information, you'd need actual measurements or additional given information.

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