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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 391 · 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.In triangle ABC, angle A = 46° and angle B = 79°. What is angle C (in degrees)?
  2. 2.The two interior opposite angles of a triangle are 71° and 30°. What is the exterior angle (in degrees)?
  3. 3.In an isosceles triangle, the two equal angles are 68° each. What is the third angle (in degrees)?
  4. 4.The two shorter sides of a right-angled triangle are 15 cm and 8 cm. How long is the longest side (in cm)?
  5. 5.The two interior opposite angles of a triangle are 65° and 40°. What is the exterior angle (in degrees)?
  6. 6.In a right-angled triangle, one of the other two angles is 46°. What is the third angle (in degrees)?
  7. 7.An exterior angle of a triangle is 82°. One of its two interior opposite angles is 24°. What is the other one (in degrees)?
  8. 8.The angles of a triangle are in the ratio 3 : 4 : 5. What is the biggest angle (in degrees)?
  9. 9.In an isosceles triangle, the two equal angles are 79° each. What is the third angle (in degrees)?
  10. 10.In triangle ABC, angle A = 69° and angle B = 55°. What is angle C (in degrees)?
  11. 11.Can a triangle have sides of 16 cm, 8 cm and 7 cm? (a) Yes (b) No
  12. 12.In triangle ABC, angle A = 38° and angle B = 76°. What is angle C (in degrees)?
  13. 13.In a right-angled triangle, one of the other two angles is 11°. What is the third angle (in degrees)?
  14. 14.The two interior opposite angles of a triangle are 45° and 28°. What is the exterior angle (in degrees)?
  15. 15.In a right-angled triangle, one of the other two angles is 74°. What is the third angle (in degrees)?
  16. 16.Can a triangle have sides of 11 cm, 7 cm and 10 cm? (a) Yes (b) No
  17. 17.Can a triangle have sides of 17 cm, 10 cm and 7 cm? (a) Yes (b) No
  18. 18.Can a triangle have sides of 15 cm, 8 cm and 3 cm? (a) Yes (b) No
  19. 19.In a right-angled triangle, one of the other two angles is 22°. What is the third angle (in degrees)?
  20. 20.In triangle ABC, angle A = 100° and angle B = 31°. What is angle C (in degrees)?
  21. 21.An exterior angle of a triangle is 68°. One of its two interior opposite angles is 35°. What is the other one (in degrees)?
  22. 22.In an isosceles triangle, the angle between the two equal sides is 60°. What is each of the other two angles (in degrees)?
  23. 23.The two interior opposite angles of a triangle are 54° and 65°. What is the exterior angle (in degrees)?
  24. 24.An exterior angle of a triangle is 145°. One of its two interior opposite angles is 67°. What is the other one (in degrees)?
  25. 25.In triangle ABC, angle A = 33° and angle B = 68°. What is angle C (in degrees)?
  26. 26.In triangle ABC, angle A = 73° and angle B = 23°. What is angle C (in degrees)?
  27. 27.The two shorter sides of a right-angled triangle are 20 cm and 15 cm. How long is the longest side (in cm)?
  28. 28.In an isosceles triangle, the angle between the two equal sides is 136°. What is each of the other two angles (in degrees)?
  29. 29.The longest side of a right-angled triangle is 10 cm and one of the other sides is 6 cm. How long is the third side (in cm)?
  30. 30.An exterior angle of a triangle is 89°. One of its two interior opposite angles is 31°. What is the other one (in degrees)?
  31. 31.In a right-angled triangle, one of the other two angles is 14°. What is the third angle (in degrees)?
  32. 32.In a right-angled triangle, one of the other two angles is 17°. What is the third angle (in degrees)?
  33. 33.In a right-angled triangle, one of the other two angles is 59°. What is the third angle (in degrees)?
  34. 34.In an isosceles triangle, the angle between the two equal sides is 34°. What is each of the other two angles (in degrees)?
  35. 35.Can a triangle have sides of 12 cm, 5 cm and 2 cm? (a) No (b) Yes
  36. 36.The two interior opposite angles of a triangle are 60° and 29°. What is the exterior angle (in degrees)?
  37. 37.In a right-angled triangle, one of the other two angles is 41°. What is the third angle (in degrees)?
  38. 38.In triangle ABC, angle A = 47° and angle B = 86°. What is angle C (in degrees)?
  39. 39.In an isosceles triangle, the angle between the two equal sides is 142°. What is each of the other two angles (in degrees)?
  40. 40.The longest side of a right-angled triangle is 17 cm and one of the other sides is 8 cm. How long is the third side (in cm)?

Answer key

  1. 55
  2. 101
  3. 44
  4. 17
  5. 105
  6. 44
  7. 58
  8. 75
  9. 22
  10. 56
  11. No
  12. 66
  13. 79
  14. 73
  15. 16
  16. Yes
  17. No
  18. No
  19. 68
  20. 49
  21. 33
  22. 60
  23. 119
  24. 78
  25. 79
  26. 84
  27. 25
  28. 22
  29. 8
  30. 58
  31. 76
  32. 73
  33. 31
  34. 73
  35. No
  36. 89
  37. 49
  38. 47
  39. 19
  40. 15

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