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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 59 · 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 6 cm, 6 cm and 13 cm? (a) Yes (b) No
  2. 2.The longest side of a right-angled triangle is 26 cm and one of the other sides is 10 cm. How long is the third side (in cm)?
  3. 3.In triangle ABC, angle A = 60° and angle B = 93°. What is angle C (in degrees)?
  4. 4.In triangle ABC, angle A = 42° and angle B = 26°. What is angle C (in degrees)?
  5. 5.In triangle ABC, angle A = 83° and angle B = 38°. What is angle C (in degrees)?
  6. 6.In a right-angled triangle, one of the other two angles is 21°. What is the third angle (in degrees)?
  7. 7.In a right-angled triangle, one of the other two angles is 20°. What is the third angle (in degrees)?
  8. 8.In triangle ABC, angle A = 84° and angle B = 61°. What is angle C (in degrees)?
  9. 9.The longest side of a right-angled triangle is 13 cm and one of the other sides is 12 cm. How long is the third side (in cm)?
  10. 10.In triangle ABC, angle A = 37° and angle B = 93°. What is angle C (in degrees)?
  11. 11.The angles of a triangle are in the ratio 2 : 2 : 5. What is the biggest angle (in degrees)?
  12. 12.In an isosceles triangle, the angle between the two equal sides is 142°. What is each of the other two angles (in degrees)?
  13. 13.In an isosceles triangle, the angle between the two equal sides is 52°. What is each of the other two angles (in degrees)?
  14. 14.In a right-angled triangle, one of the other two angles is 32°. What is the third angle (in degrees)?
  15. 15.In an isosceles triangle, the angle between the two equal sides is 126°. What is each of the other two angles (in degrees)?
  16. 16.In triangle ABC, angle A = 67° and angle B = 22°. What is angle C (in degrees)?
  17. 17.The angles of a triangle are in the ratio 3 : 5 : 7. What is the smallest angle (in degrees)?
  18. 18.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)?
  19. 19.The angles of a triangle are in the ratio 1 : 2 : 2. What is the biggest angle (in degrees)?
  20. 20.An exterior angle of a triangle is 111°. One of its two interior opposite angles is 70°. What is the other one (in degrees)?
  21. 21.In an isosceles triangle, the two equal angles are 24° each. What is the third angle (in degrees)?
  22. 22.In a right-angled triangle, one of the other two angles is 76°. What is the third angle (in degrees)?
  23. 23.Can a triangle have sides of 11 cm, 9 cm and 24 cm? (a) Yes (b) No
  24. 24.An exterior angle of a triangle is 122°. One of its two interior opposite angles is 43°. What is the other one (in degrees)?
  25. 25.In triangle ABC, angle A = 92° and angle B = 61°. What is angle C (in degrees)?
  26. 26.The two shorter sides of a right-angled triangle are 7 cm and 24 cm. How long is the longest side (in cm)?
  27. 27.An exterior angle of a triangle is 109°. One of its two interior opposite angles is 58°. What is the other one (in degrees)?
  28. 28.In a right-angled triangle, one of the other two angles is 77°. What is the third angle (in degrees)?
  29. 29.An exterior angle of a triangle is 78°. One of its two interior opposite angles is 40°. What is the other one (in degrees)?
  30. 30.In an isosceles triangle, the angle between the two equal sides is 26°. What is each of the other two angles (in degrees)?
  31. 31.The angles of a triangle are in the ratio 1 : 1 : 2. What is the biggest angle (in degrees)?
  32. 32.Can a triangle have sides of 11 cm, 8 cm and 19 cm? (a) No (b) Yes
  33. 33.In triangle ABC, angle A = 42° and angle B = 108°. What is angle C (in degrees)?
  34. 34.In a right-angled triangle, one of the other two angles is 51°. What is the third angle (in degrees)?
  35. 35.An exterior angle of a triangle is 117°. One of its two interior opposite angles is 57°. What is the other one (in degrees)?
  36. 36.Can a triangle have sides of 2 cm, 12 cm and 12 cm? (a) Yes (b) No
  37. 37.In triangle ABC, angle A = 86° and angle B = 69°. What is angle C (in degrees)?
  38. 38.Can a triangle have sides of 5 cm, 7 cm and 4 cm? (a) No (b) Yes
  39. 39.The two shorter sides of a right-angled triangle are 10 cm and 24 cm. How long is the longest side (in cm)?
  40. 40.The longest side of a right-angled triangle is 17 cm and one of the other sides is 15 cm. How long is the third side (in cm)?

Answer key

  1. No
  2. 24
  3. 27
  4. 112
  5. 59
  6. 69
  7. 70
  8. 35
  9. 5
  10. 50
  11. 100
  12. 19
  13. 64
  14. 58
  15. 27
  16. 91
  17. 36
  18. 15
  19. 72
  20. 41
  21. 132
  22. 14
  23. No
  24. 79
  25. 27
  26. 25
  27. 51
  28. 13
  29. 38
  30. 77
  31. 90
  32. No
  33. 30
  34. 39
  35. 60
  36. Yes
  37. 25
  38. Yes
  39. 26
  40. 8

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