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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 281 · 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 two shorter sides of a right-angled triangle are 12 cm and 9 cm. How long is the longest side (in cm)?
  2. 2.The angles of a triangle are in the ratio 2 : 3 : 5. What is the smallest angle (in degrees)?
  3. 3.In an isosceles triangle, the angle between the two equal sides is 142°. What is each of the other two angles (in degrees)?
  4. 4.An exterior angle of a triangle is 81°. One of its two interior opposite angles is 23°. What is the other one (in degrees)?
  5. 5.In an isosceles triangle, the two equal angles are 41° each. What is the third angle (in degrees)?
  6. 6.The longest side of a right-angled triangle is 5 cm and one of the other sides is 3 cm. How long is the third side (in cm)?
  7. 7.In an isosceles triangle, the two equal angles are 68° each. What is the third angle (in degrees)?
  8. 8.The longest side of a right-angled triangle is 39 cm and one of the other sides is 36 cm. How long is the third side (in cm)?
  9. 9.The angles of a triangle are in the ratio 1 : 2 : 3. What is the biggest angle (in degrees)?
  10. 10.The angles of a triangle are in the ratio 2 : 7 : 9. What is the biggest angle (in degrees)?
  11. 11.The angles of a triangle are in the ratio 4 : 5 : 6. What is the biggest angle (in degrees)?
  12. 12.Can a triangle have sides of 8 cm, 2 cm and 9 cm? (a) Yes (b) No
  13. 13.In triangle ABC, angle A = 97° and angle B = 62°. What is angle C (in degrees)?
  14. 14.The longest side of a right-angled triangle is 25 cm and one of the other sides is 20 cm. How long is the third side (in cm)?
  15. 15.The two shorter sides of a right-angled triangle are 12 cm and 5 cm. How long is the longest side (in cm)?
  16. 16.The two shorter sides of a right-angled triangle are 6 cm and 8 cm. How long is the longest side (in cm)?
  17. 17.In a right-angled triangle, one of the other two angles is 60°. What is the third angle (in degrees)?
  18. 18.In triangle ABC, angle A = 64° and angle B = 67°. What is angle C (in degrees)?
  19. 19.The angles of a triangle are in the ratio 2 : 3 : 4. What is the biggest angle (in degrees)?
  20. 20.In a right-angled triangle, one of the other two angles is 63°. What is the third angle (in degrees)?
  21. 21.Can a triangle have sides of 10 cm, 22 cm and 7 cm? (a) No (b) Yes
  22. 22.Can a triangle have sides of 5 cm, 5 cm and 13 cm? (a) Yes (b) No
  23. 23.In triangle ABC, angle A = 58° and angle B = 83°. What is angle C (in degrees)?
  24. 24.In a right-angled triangle, one of the other two angles is 16°. What is the third angle (in degrees)?
  25. 25.The angles of a triangle are in the ratio 3 : 3 : 4. What is the biggest angle (in degrees)?
  26. 26.The angles of a triangle are in the ratio 1 : 3 : 5. What is the smallest angle (in degrees)?
  27. 27.Can a triangle have sides of 11 cm, 10 cm and 5 cm? (a) No (b) Yes
  28. 28.In triangle ABC, angle A = 62° and angle B = 52°. What is angle C (in degrees)?
  29. 29.Can a triangle have sides of 9 cm, 6 cm and 17 cm? (a) No (b) Yes
  30. 30.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)?
  31. 31.In an isosceles triangle, the two equal angles are 55° each. What is the third angle (in degrees)?
  32. 32.The two interior opposite angles of a triangle are 51° and 25°. What is the exterior angle (in degrees)?
  33. 33.In triangle ABC, angle A = 82° and angle B = 44°. What is angle C (in degrees)?
  34. 34.In triangle ABC, angle A = 71° and angle B = 55°. What is angle C (in degrees)?
  35. 35.Can a triangle have sides of 5 cm, 12 cm and 12 cm? (a) No (b) Yes
  36. 36.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)?
  37. 37.The angles of a triangle are in the ratio 2 : 2 : 5. What is the biggest angle (in degrees)?
  38. 38.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)?
  39. 39.In triangle ABC, angle A = 84° and angle B = 63°. What is angle C (in degrees)?
  40. 40.In a right-angled triangle, one of the other two angles is 61°. What is the third angle (in degrees)?

Answer key

  1. 15
  2. 36
  3. 19
  4. 58
  5. 98
  6. 4
  7. 44
  8. 15
  9. 90
  10. 90
  11. 72
  12. Yes
  13. 21
  14. 15
  15. 13
  16. 10
  17. 30
  18. 49
  19. 80
  20. 27
  21. No
  22. No
  23. 39
  24. 74
  25. 72
  26. 20
  27. Yes
  28. 66
  29. No
  30. 12
  31. 70
  32. 76
  33. 54
  34. 54
  35. Yes
  36. 7
  37. 100
  38. 15
  39. 33
  40. 29

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