Properties of Triangles

Name: ___________________________

Date: ___________________________

Remember: Equilateral triangles have 3 equal sides and 3 equal angles (60° each). Isosceles triangles have 2 equal sides and 2 equal angles. Scalene triangles have no equal sides and no equal angles.

Part A: Classify each triangle

Write whether each triangle is equilateral, isosceles, or scalene.

1. A triangle with sides 5 cm, 5 cm, and 8 cm: _______________________

2. A triangle with sides 7 cm, 9 cm, and 11 cm: _______________________

3. A triangle with all angles measuring 60°: _______________________

4. A triangle with sides 12 m, 12 m, and 12 m: _______________________

5. A triangle with angles 45°, 65°, and 70°: _______________________

6. A triangle with two angles of 55° each: _______________________

Part B: Finding missing angles

Find the missing angle in each triangle. (Remember: angles in a triangle sum to 180°)

7. Equilateral triangle: All angles = ______°

8. Isosceles triangle with angles 70°, 70°, and ?: Missing angle = ______°

9. Triangle with angles 35° and 85°: Missing angle = ______°

10. Isosceles triangle with angles 40°, ?, and ?: Two missing angles = ______°

Part C: True or False

Write T for true or F for false.

11. An equilateral triangle is also an isosceles triangle. ______

12. A scalene triangle can have two equal angles. ______

13. An isosceles triangle has at least two equal sides. ______

14. All equilateral triangles have angles of 60°. ______

15. A triangle can have sides of 2 cm, 3 cm, and 10 cm. ______

Part D: Problem solving

16. The perimeter of an equilateral triangle is 24 cm. What is the length of each side?

Answer: ___________________________

17. An isosceles triangle has two equal sides of 9 cm each. If the perimeter is 25 cm, what is the length of the third side?

Answer: ___________________________