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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 55 · 40 sums
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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 = 47° and angle B = 31°. What is angle C (in degrees)?
  2. 2.Can a triangle have sides of 7 cm, 6 cm and 6 cm? (a) No (b) Yes
  3. 3.In triangle ABC, angle A = 45° and angle B = 85°. What is angle C (in degrees)?
  4. 4.The longest side of a right-angled triangle is 25 cm and one of the other sides is 24 cm. How long is the third side (in cm)?
  5. 5.Can a triangle have sides of 21 cm, 6 cm and 11 cm? (a) No (b) Yes
  6. 6.In a right-angled triangle, one of the other two angles is 68°. What is the third angle (in degrees)?
  7. 7.The angles of a triangle are in the ratio 3 : 3 : 4. What is the biggest angle (in degrees)?
  8. 8.An exterior angle of a triangle is 95°. One of its two interior opposite angles is 55°. What is the other one (in degrees)?
  9. 9.In an isosceles triangle, the two equal angles are 52° each. What is the third angle (in degrees)?
  10. 10.In triangle ABC, angle A = 61° and angle B = 33°. What is angle C (in degrees)?
  11. 11.In a right-angled triangle, one of the other two angles is 28°. What is the third angle (in degrees)?
  12. 12.In a right-angled triangle, one of the other two angles is 20°. What is the third angle (in degrees)?
  13. 13.In a right-angled triangle, one of the other two angles is 23°. What is the third angle (in degrees)?
  14. 14.In an isosceles triangle, the angle between the two equal sides is 124°. What is each of the other two angles (in degrees)?
  15. 15.In an isosceles triangle, the two equal angles are 75° each. What is the third angle (in degrees)?
  16. 16.The two interior opposite angles of a triangle are 21° and 65°. What is the exterior angle (in degrees)?
  17. 17.In triangle ABC, angle A = 35° and angle B = 77°. What is angle C (in degrees)?
  18. 18.Can a triangle have sides of 4 cm, 10 cm and 18 cm? (a) Yes (b) No
  19. 19.An exterior angle of a triangle is 121°. One of its two interior opposite angles is 41°. What is the other one (in degrees)?
  20. 20.In triangle ABC, angle A = 96° and angle B = 24°. What is angle C (in degrees)?
  21. 21.In an isosceles triangle, the angle between the two equal sides is 58°. What is each of the other two angles (in degrees)?
  22. 22.In triangle ABC, angle A = 23° and angle B = 40°. What is angle C (in degrees)?
  23. 23.Can a triangle have sides of 20 cm, 8 cm and 8 cm? (a) Yes (b) No
  24. 24.In a right-angled triangle, one of the other two angles is 67°. What is the third angle (in degrees)?
  25. 25.In a right-angled triangle, one of the other two angles is 36°. What is the third angle (in degrees)?
  26. 26.The longest side of a right-angled triangle is 25 cm and one of the other sides is 7 cm. How long is the third side (in cm)?
  27. 27.The two shorter sides of a right-angled triangle are 18 cm and 24 cm. How long is the longest side (in cm)?
  28. 28.In an isosceles triangle, the angle between the two equal sides is 64°. What is each of the other two angles (in degrees)?
  29. 29.In triangle ABC, angle A = 30° and angle B = 31°. What is angle C (in degrees)?
  30. 30.In an isosceles triangle, the angle between the two equal sides is 110°. What is each of the other two angles (in degrees)?
  31. 31.In triangle ABC, angle A = 89° and angle B = 34°. What is angle C (in degrees)?
  32. 32.An exterior angle of a triangle is 122°. One of its two interior opposite angles is 68°. What is the other one (in degrees)?
  33. 33.In a right-angled triangle, one of the other two angles is 32°. What is the third angle (in degrees)?
  34. 34.In an isosceles triangle, the two equal angles are 31° each. What is the third angle (in degrees)?
  35. 35.Can a triangle have sides of 5 cm, 4 cm and 3 cm? (a) No (b) Yes
  36. 36.An exterior angle of a triangle is 106°. One of its two interior opposite angles is 51°. What is the other one (in degrees)?
  37. 37.The two interior opposite angles of a triangle are 71° and 75°. What is the exterior angle (in degrees)?
  38. 38.An exterior angle of a triangle is 58°. One of its two interior opposite angles is 34°. What is the other one (in degrees)?
  39. 39.An exterior angle of a triangle is 71°. One of its two interior opposite angles is 31°. What is the other one (in degrees)?
  40. 40.The angles of a triangle are in the ratio 5 : 6 : 7. What is the smallest angle (in degrees)?

Answer key

  1. 102
  2. Yes
  3. 50
  4. 7
  5. No
  6. 22
  7. 72
  8. 40
  9. 76
  10. 86
  11. 62
  12. 70
  13. 67
  14. 28
  15. 30
  16. 86
  17. 68
  18. No
  19. 80
  20. 60
  21. 61
  22. 117
  23. No
  24. 23
  25. 54
  26. 24
  27. 30
  28. 58
  29. 119
  30. 35
  31. 57
  32. 54
  33. 58
  34. 118
  35. Yes
  36. 55
  37. 146
  38. 24
  39. 40
  40. 50

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