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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 816 · 40 sums
TalentJR

The method (Inside 180, outside the sum): Angle sum: ∠A + ∠B + ∠C = 180°. Exterior angle = sum of the two interior opposite angles. Right-angled triangle: longest side² = side² + side² (3, 4, 5 and 5, 12, 13 are famous sets). Sides can make a triangle only if the two shorter sides add up to more than the longest side.

NameDateTime takenScore ___ / 40
  1. 1.The angles of a triangle are in the ratio 1 : 2 : 3. What is the smallest angle (in degrees)?
  2. 2.In triangle ABC, angle A = 29° and angle B = 85°. What is angle C (in degrees)?
  3. 3.Can a triangle have sides of 17 cm, 8 cm and 6 cm? (a) No (b) Yes
  4. 4.In a right-angled triangle, one of the other two angles is 14°. What is the third angle (in degrees)?
  5. 5.In an isosceles triangle, the two equal angles are 20° each. What is the third angle (in degrees)?
  6. 6.In an isosceles triangle, the angle between the two equal sides is 106°. What is each of the other two angles (in degrees)?
  7. 7.In triangle ABC, angle A = 25° and angle B = 25°. What is angle C (in degrees)?
  8. 8.In triangle ABC, angle A = 35° and angle B = 85°. What is angle C (in degrees)?
  9. 9.An exterior angle of a triangle is 71°. One of its two interior opposite angles is 29°. What is the other one (in degrees)?
  10. 10.The angles of a triangle are in the ratio 2 : 2 : 5. What is the smallest angle (in degrees)?
  11. 11.Can a triangle have sides of 3 cm, 19 cm and 11 cm? (a) No (b) Yes
  12. 12.In triangle ABC, angle A = 49° and angle B = 55°. What is angle C (in degrees)?
  13. 13.The angles of a triangle are in the ratio 3 : 5 : 7. What is the smallest angle (in degrees)?
  14. 14.In triangle ABC, angle A = 91° and angle B = 30°. What is angle C (in degrees)?
  15. 15.In an isosceles triangle, the angle between the two equal sides is 100°. What is each of the other two angles (in degrees)?
  16. 16.An exterior angle of a triangle is 119°. One of its two interior opposite angles is 51°. What is the other one (in degrees)?
  17. 17.In triangle ABC, angle A = 70° and angle B = 80°. What is angle C (in degrees)?
  18. 18.The two interior opposite angles of a triangle are 58° and 54°. What is the exterior angle (in degrees)?
  19. 19.The two interior opposite angles of a triangle are 51° and 28°. What is the exterior angle (in degrees)?
  20. 20.In an isosceles triangle, the two equal angles are 82° each. What is the third angle (in degrees)?
  21. 21.In triangle ABC, angle A = 38° and angle B = 33°. What is angle C (in degrees)?
  22. 22.The longest side of a right-angled triangle is 13 cm and one of the other sides is 5 cm. How long is the third side (in cm)?
  23. 23.In a right-angled triangle, one of the other two angles is 42°. What is the third angle (in degrees)?
  24. 24.An exterior angle of a triangle is 102°. One of its two interior opposite angles is 25°. What is the other one (in degrees)?
  25. 25.In an isosceles triangle, the two equal angles are 74° each. What is the third angle (in degrees)?
  26. 26.The longest side of a right-angled triangle is 15 cm and one of the other sides is 12 cm. How long is the third side (in cm)?
  27. 27.Can a triangle have sides of 6 cm, 6 cm and 17 cm? (a) No (b) Yes
  28. 28.In an isosceles triangle, the angle between the two equal sides is 126°. What is each of the other two angles (in degrees)?
  29. 29.Can a triangle have sides of 7 cm, 3 cm and 7 cm? (a) No (b) Yes
  30. 30.Can a triangle have sides of 9 cm, 9 cm and 23 cm? (a) Yes (b) No
  31. 31.Can a triangle have sides of 6 cm, 15 cm and 8 cm? (a) Yes (b) No
  32. 32.The angles of a triangle are in the ratio 1 : 1 : 2. What is the biggest angle (in degrees)?
  33. 33.The two interior opposite angles of a triangle are 33° and 50°. What is the exterior angle (in degrees)?
  34. 34.The two interior opposite angles of a triangle are 73° and 71°. What is the exterior angle (in degrees)?
  35. 35.In an isosceles triangle, the two equal angles are 29° each. What is the third angle (in degrees)?
  36. 36.In an isosceles triangle, the angle between the two equal sides is 102°. What is each of the other two angles (in degrees)?
  37. 37.In a right-angled triangle, one of the other two angles is 47°. What is the third angle (in degrees)?
  38. 38.In a right-angled triangle, one of the other two angles is 55°. What is the third angle (in degrees)?
  39. 39.In an isosceles triangle, the two equal angles are 42° each. What is the third angle (in degrees)?
  40. 40.The two interior opposite angles of a triangle are 62° and 35°. What is the exterior angle (in degrees)?

Answer key

  1. 30
  2. 66
  3. No
  4. 76
  5. 140
  6. 37
  7. 130
  8. 60
  9. 42
  10. 40
  11. No
  12. 76
  13. 36
  14. 59
  15. 40
  16. 68
  17. 30
  18. 112
  19. 79
  20. 16
  21. 109
  22. 12
  23. 48
  24. 77
  25. 32
  26. 9
  27. No
  28. 27
  29. Yes
  30. No
  31. No
  32. 90
  33. 83
  34. 144
  35. 122
  36. 39
  37. 43
  38. 35
  39. 96
  40. 97

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