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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 809 · 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.Can a triangle have sides of 9 cm, 6 cm and 12 cm? (a) No (b) Yes
  2. 2.In triangle ABC, angle A = 31° and angle B = 114°. What is angle C (in degrees)?
  3. 3.In an isosceles triangle, the two equal angles are 69° each. What is the third angle (in degrees)?
  4. 4.In a right-angled triangle, one of the other two angles is 28°. What is the third angle (in degrees)?
  5. 5.The angles of a triangle are in the ratio 3 : 4 : 5. What is the smallest angle (in degrees)?
  6. 6.An exterior angle of a triangle is 110°. One of its two interior opposite angles is 62°. What is the other one (in degrees)?
  7. 7.In triangle ABC, angle A = 40° and angle B = 57°. What is angle C (in degrees)?
  8. 8.Can a triangle have sides of 6 cm, 3 cm and 3 cm? (a) No (b) Yes
  9. 9.Can a triangle have sides of 13 cm, 8 cm and 8 cm? (a) No (b) Yes
  10. 10.The two interior opposite angles of a triangle are 32° and 42°. What is the exterior angle (in degrees)?
  11. 11.In an isosceles triangle, the two equal angles are 20° each. What is the third angle (in degrees)?
  12. 12.The angles of a triangle are in the ratio 1 : 4 : 5. What is the smallest angle (in degrees)?
  13. 13.In an isosceles triangle, the angle between the two equal sides is 50°. What is each of the other two angles (in degrees)?
  14. 14.The angles of a triangle are in the ratio 1 : 4 : 5. What is the biggest angle (in degrees)?
  15. 15.In an isosceles triangle, the angle between the two equal sides is 20°. What is each of the other two angles (in degrees)?
  16. 16.In triangle ABC, angle A = 27° and angle B = 30°. What is angle C (in degrees)?
  17. 17.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)?
  18. 18.The angles of a triangle are in the ratio 5 : 6 : 7. What is the biggest angle (in degrees)?
  19. 19.In an isosceles triangle, the two equal angles are 27° each. What is the third angle (in degrees)?
  20. 20.Can a triangle have sides of 9 cm, 5 cm and 9 cm? (a) No (b) Yes
  21. 21.An exterior angle of a triangle is 115°. One of its two interior opposite angles is 41°. What is the other one (in degrees)?
  22. 22.In triangle ABC, angle A = 62° and angle B = 31°. What is angle C (in degrees)?
  23. 23.The two interior opposite angles of a triangle are 37° and 61°. What is the exterior angle (in degrees)?
  24. 24.Can a triangle have sides of 10 cm, 20 cm and 7 cm? (a) Yes (b) No
  25. 25.In an isosceles triangle, the angle between the two equal sides is 134°. What is each of the other two angles (in degrees)?
  26. 26.The angles of a triangle are in the ratio 2 : 3 : 5. What is the biggest angle (in degrees)?
  27. 27.In triangle ABC, angle A = 85° and angle B = 32°. What is angle C (in degrees)?
  28. 28.In a right-angled triangle, one of the other two angles is 43°. What is the third angle (in degrees)?
  29. 29.In triangle ABC, angle A = 34° and angle B = 111°. What is angle C (in degrees)?
  30. 30.In triangle ABC, angle A = 56° and angle B = 52°. What is angle C (in degrees)?
  31. 31.The angles of a triangle are in the ratio 4 : 5 : 6. What is the smallest angle (in degrees)?
  32. 32.In an isosceles triangle, the angle between the two equal sides is 62°. What is each of the other two angles (in degrees)?
  33. 33.Can a triangle have sides of 9 cm, 19 cm and 9 cm? (a) No (b) Yes
  34. 34.In an isosceles triangle, the two equal angles are 29° each. What is the third angle (in degrees)?
  35. 35.In an isosceles triangle, the two equal angles are 46° each. What is the third angle (in degrees)?
  36. 36.In triangle ABC, angle A = 52° and angle B = 75°. What is angle C (in degrees)?
  37. 37.In an isosceles triangle, the angle between the two equal sides is 158°. What is each of the other two angles (in degrees)?
  38. 38.In a right-angled triangle, one of the other two angles is 35°. What is the third angle (in degrees)?
  39. 39.Can a triangle have sides of 18 cm, 8 cm and 8 cm? (a) No (b) Yes
  40. 40.In triangle ABC, angle A = 20° and angle B = 71°. What is angle C (in degrees)?

Answer key

  1. Yes
  2. 35
  3. 42
  4. 62
  5. 45
  6. 48
  7. 83
  8. No
  9. Yes
  10. 74
  11. 140
  12. 18
  13. 65
  14. 90
  15. 80
  16. 123
  17. 7
  18. 70
  19. 126
  20. Yes
  21. 74
  22. 87
  23. 98
  24. No
  25. 23
  26. 90
  27. 63
  28. 47
  29. 35
  30. 72
  31. 48
  32. 59
  33. No
  34. 122
  35. 88
  36. 53
  37. 11
  38. 55
  39. No
  40. 89

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