Identifying Types of Triangles - Answer Key - Acute, Obtuse, Right and Equilateral, Isosceles, Scalene

Sep 30, 2026

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Worksheet answer key for identifying triangle types by both angle measures and side/angle equality. It defines acute, obtuse, and right triangles using the 90° angle threshold, and defines equilateral, isosceles, and scalene triangles using counts of equal sides and equal angles. The key lists classifications for multiple numbered items, pairing each triangle’s angle type (A/O/R) with its side/angle type (E/I/S), supporting quick checking and targeted review.

LanguageEnglish

CategoryExam

FormatPDF

Pages3

Reading Time8 min

AccessFree to download

Determine Triangle Types

Angle-based classification (A, O, R)

Side/angle-based classification (E, I, S)

Identifying Types of Triangles Name: | Determine if each triangle is acute(A), obtuse(O) or right(R) and if it is an

equilateral(E), isosceles(I) or scalene(S). Acute Triangle:
All angles are less than 90° .
Obtuse Triangle:
One angle is greater than 90° .
Right Triangle:
One angle is 90° .
Equilateral Triangle:
3 equal sides. 3 equal angles.
Isosceles Triangle:
2 equal sides. 2 equal angles.
Scalene Triangle:
No equal sides. No equal angles.

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8. | | Answers | | | | | | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | 1-8 | 88 | 75 | 63 | 50 | | 38 | 25 | 13 | 0 | [Math](Math www.CommonCoreSheets.com 5)[ www.CommonCoreSheets.com](Math www.CommonCoreSheets.com 5)[ 5](Math www.CommonCoreSheets.com 5) Identifying Types of Triangles Name: Answer Key | Determine if each triangle is acute(A), obtuse(O) or right(R) and if it is an

equilateral(E), isosceles(I) or scalene(S). Acute Triangle:
All angles are less than 90° .
Obtuse Triangle:
One angle is greater than 90° .
Right Triangle:
One angle is 90° .
Equilateral Triangle:
3 equal sides. 3 equal angles.
Isosceles Triangle:
2 equal sides. 2 equal angles.
Scalene Triangle:
No equal sides. No equal angles.

| | | | Answers 1. A E 2. R S 3. O I 4. A S 5. O I 6. A I 7. O S 8. R I | | | | | | | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | | 1) 150
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158 135
~~ 114 ~~

8) 150
150
| | | | | | | | | | 1-8 | | 88 | 75 | 63 | 50 | 38 | 25 | 13 | 0 | [Math](Math www.CommonCoreSheets.com 5)[ www.CommonCoreSheets.com](Math www.CommonCoreSheets.com 5)[ 5](Math www.CommonCoreSheets.com 5) Identifying Types of Triangles Name: | Determine if each triangle is acute(A), obtuse(O) or right(R) and if it is an

equilateral(E), isosceles(I) or scalene(S). Acute Triangle:
All angles are less than 90° .
Obtuse Triangle:
One angle is greater than 90° .
Right Triangle:
One angle is 90° .
Equilateral Triangle:
3 equal sides. 3 equal angles.
Isosceles Triangle:
2 equal sides. 2 equal angles.
Scalene Triangle:
No equal sides. No equal angles.

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6. | | Answers | | | | | | --- | --- | --- | --- | --- | --- | --- | --- | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | 1-6 | 83 | 67 | | 50 | 33 | 17 | 0 | Math Modified [www.CommonCoreSheets.com](www.CommonCoreSheets.com) 5

FAQs

How are acute, obtuse, and right triangles identified?

Acute triangles have all angles less than 90°. Obtuse triangles have one angle greater than 90°. Right triangles have one angle equal to 90°.

How are equilateral, isosceles, and scalene triangles identified?

Equilateral triangles have 3 equal sides and 3 equal angles. Isosceles triangles have 2 equal sides and 2 equal angles. Scalene triangles have no equal sides and no equal angles.

What does the answer key provide for the numbered triangles?

For each numbered triangle, the key gives both its angle classification (A, O, or R) and its side/angle classification (E, I, or S) so answers can be checked quickly.

Sep 30, 2026

Uploaded by Fans