Identify the Triangle Type: Given Sides 9, 9, and 5

Triangle Classification with Equal Side Lengths

What kind of triangle is given in the drawing?

999555999AAABBBCCC

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:00 Identify which type of triangle is shown in the drawing
00:04 Size of sides according to the given data
00:07 A triangle with two equal legs is an isosceles triangle
00:12 This is the solution

Step-by-step written solution

Follow each step carefully to understand the complete solution
1

Understand the problem

What kind of triangle is given in the drawing?

999555999AAABBBCCC

2

Step-by-step solution

Given that sides AB and AC are both equal to 9, which means that the legs of the triangle are equal and the base BC is equal to 5,

Therefore, the triangle is isosceles.

3

Final Answer

Isosceles triangle

Key Points to Remember

Essential concepts to master this topic
  • Definition: Isosceles triangles have exactly two sides of equal length
  • Method: Compare all three sides: 9, 9, 5 shows two equal sides
  • Verify: Two sides equal (9 = 9) and third different (5 ≠ 9) confirms isosceles ✓

Common Mistakes

Avoid these frequent errors
  • Confusing isosceles with equilateral triangles
    Don't assume a triangle is equilateral just because two sides are equal = wrong classification! Equilateral means ALL three sides are equal. Always check if the third side matches the other two before deciding.

Practice Quiz

Test your knowledge with interactive questions

Is the triangle in the drawing a right triangle?

FAQ

Everything you need to know about this question

What's the difference between isosceles and equilateral triangles?

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Isosceles triangles have exactly two equal sides, while equilateral triangles have all three sides equal. In this case, 9, 9, 5 shows two equal sides, making it isosceles.

How do I remember which triangle type is which?

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Think of it like this: Scalene = all different, Isosceles = two same, Equilateral = all same. Count how many sides match!

Can a triangle have sides 9, 9, and 18?

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No! This violates the triangle inequality. The sum of any two sides must be greater than the third side. Here, 9 + 9 = 18, which equals (not greater than) the third side.

What if I can't tell which sides are equal from the drawing?

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Always look for the numerical labels on each side rather than trying to judge by eye. Drawings aren't always to scale, but the numbers tell you the exact lengths.

Does the position of equal sides matter?

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Not at all! Whether the equal sides are adjacent (next to each other) or opposite doesn't change the classification. Two equal sides anywhere makes it isosceles.

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