Comparing Angles in an Equilateral Triangle: Which is Larger, ∢B or ∢A?

Angle Properties with Equilateral Triangles

ABC is an equilateral triangle.

Which angle is larger, B ∢B orA ∢A ?

AAABBBCCC

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Step-by-step video solution

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00:00 Which angle is larger - A\B?
00:06 Equilateral triangle according to the given
00:12 In an equilateral triangle all angles are equal
00:31 In an equilateral triangle all angles are equal to 60
00:39 And this is the solution to the question

Step-by-step written solution

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1

Understand the problem

ABC is an equilateral triangle.

Which angle is larger, B ∢B orA ∢A ?

AAABBBCCC

2

Step-by-step solution

In this problem, we need to determine which angle is larger between B ∢B and A ∢A in the equilateral triangle ABC \triangle ABC .

Let's start by recalling what an equilateral triangle is. In an equilateral triangle, all three sides have equal length, and consequently, all three internal angles are of equal measure. This is a fundamental property of equilateral triangles.

Since ABC \triangle ABC is equilateral, we know that each angle, including B ∢B and A ∢A , measures 60 60^\circ . This is because the sum of internal angles in any triangle is 180 180^\circ , and in an equilateral triangle, this total is divided equally among the three angles. Thus:
A=B=C=1803=60. \begin{aligned} ∢A &= ∢B = ∢C = \frac{180^\circ}{3} = 60^\circ. \end{aligned}

Since both A ∢A and B ∢B are 60 60^\circ , neither angle is larger than the other; they are equal.

This means that the correct statement regarding their measures is that A=B ∢A = ∢B .

Thus, according to the choices provided, the correct answer is:

Choice 4: A=B ∢A = ∢B .

3

Final Answer

A=B ∢A=∢B

Key Points to Remember

Essential concepts to master this topic
  • Definition: Equilateral triangles have all sides equal and all angles equal
  • Calculation: Each angle = 180° ÷ 3 = 60° in any equilateral triangle
  • Verification: Check that ∠A = ∠B = ∠C = 60° adds to 180° ✓

Common Mistakes

Avoid these frequent errors
  • Assuming angles can be different in equilateral triangles
    Don't compare individual angles as if they could be different sizes = incorrect conclusion! In equilateral triangles, equal sides automatically create equal angles due to the fundamental properties of triangles. Always remember that equilateral means ALL angles are exactly 60°.

Practice Quiz

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Is the straight line in the figure the height of the triangle?

FAQ

Everything you need to know about this question

Why are all angles in an equilateral triangle exactly 60°?

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Because the sum of angles in any triangle is 180°, and in an equilateral triangle, all three angles are equal. So each angle = 180°3=60° \frac{180°}{3} = 60° .

What's the difference between equilateral and isosceles triangles?

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Equilateral: All 3 sides equal, all 3 angles = 60°
Isosceles: Only 2 sides equal, only 2 angles equal (but not necessarily 60°)

Can I tell if angles are equal just by looking at the diagram?

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Be careful! Diagrams can be misleading. Always use the given information that ABC is equilateral. This mathematical fact tells you the angles are equal, regardless of how the drawing appears.

Do I need to measure the angles to compare them?

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No! Once you know it's an equilateral triangle, you automatically know all angles are 60°. The comparison becomes: 60° compared to 60°, which means they're equal.

What if the triangle looks like one angle is bigger?

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Trust the mathematical definition, not visual appearance! If it's stated as equilateral, then A=B=C=60° ∠A = ∠B = ∠C = 60° no matter how it's drawn.

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