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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 603 · 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 23 cm, 9 cm and 12 cm? (a) Yes (b) No
  2. 2.Can a triangle have sides of 11 cm, 20 cm and 9 cm? (a) Yes (b) No
  3. 3.The angles of a triangle are in the ratio 3 : 5 : 7. What is the biggest angle (in degrees)?
  4. 4.In a right-angled triangle, one of the other two angles is 22°. What is the third angle (in degrees)?
  5. 5.In a right-angled triangle, one of the other two angles is 45°. What is the third angle (in degrees)?
  6. 6.The two shorter sides of a right-angled triangle are 7 cm and 24 cm. How long is the longest side (in cm)?
  7. 7.The angles of a triangle are in the ratio 3 : 3 : 4. What is the biggest angle (in degrees)?
  8. 8.The angles of a triangle are in the ratio 1 : 2 : 2. What is the biggest angle (in degrees)?
  9. 9.In an isosceles triangle, the two equal angles are 34° each. What is the third angle (in degrees)?
  10. 10.In a right-angled triangle, one of the other two angles is 10°. What is the third angle (in degrees)?
  11. 11.An exterior angle of a triangle is 89°. One of its two interior opposite angles is 69°. What is the other one (in degrees)?
  12. 12.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)?
  13. 13.In a right-angled triangle, one of the other two angles is 33°. What is the third angle (in degrees)?
  14. 14.In a right-angled triangle, one of the other two angles is 38°. What is the third angle (in degrees)?
  15. 15.In triangle ABC, angle A = 24° and angle B = 55°. What is angle C (in degrees)?
  16. 16.The two shorter sides of a right-angled triangle are 8 cm and 15 cm. How long is the longest side (in cm)?
  17. 17.The angles of a triangle are in the ratio 3 : 5 : 7. What is the smallest angle (in degrees)?
  18. 18.An exterior angle of a triangle is 90°. One of its two interior opposite angles is 67°. What is the other one (in degrees)?
  19. 19.The angles of a triangle are in the ratio 5 : 6 : 7. What is the biggest angle (in degrees)?
  20. 20.In an isosceles triangle, the two equal angles are 83° each. What is the third angle (in degrees)?
  21. 21.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)?
  22. 22.In a right-angled triangle, one of the other two angles is 31°. What is the third angle (in degrees)?
  23. 23.In triangle ABC, angle A = 45° and angle B = 54°. What is angle C (in degrees)?
  24. 24.In an isosceles triangle, the two equal angles are 75° each. What is the third angle (in degrees)?
  25. 25.In triangle ABC, angle A = 35° and angle B = 46°. What is angle C (in degrees)?
  26. 26.In an isosceles triangle, the angle between the two equal sides is 52°. What is each of the other two angles (in degrees)?
  27. 27.The angles of a triangle are in the ratio 1 : 1 : 2. What is the biggest angle (in degrees)?
  28. 28.The angles of a triangle are in the ratio 4 : 5 : 6. What is the biggest angle (in degrees)?
  29. 29.In an isosceles triangle, the two equal angles are 85° each. What is the third angle (in degrees)?
  30. 30.In triangle ABC, angle A = 24° and angle B = 91°. 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.Can a triangle have sides of 5 cm, 9 cm and 9 cm? (a) No (b) Yes
  33. 33.In a right-angled triangle, one of the other two angles is 34°. What is the third angle (in degrees)?
  34. 34.In an isosceles triangle, the two equal angles are 23° each. What is the third angle (in degrees)?
  35. 35.An exterior angle of a triangle is 89°. One of its two interior opposite angles is 41°. What is the other one (in degrees)?
  36. 36.In a right-angled triangle, one of the other two angles is 77°. What is the third angle (in degrees)?
  37. 37.The angles of a triangle are in the ratio 2 : 3 : 4. What is the biggest angle (in degrees)?
  38. 38.In an isosceles triangle, the angle between the two equal sides is 26°. What is each of the other two angles (in degrees)?
  39. 39.In an isosceles triangle, the angle between the two equal sides is 106°. What is each of the other two angles (in degrees)?
  40. 40.An exterior angle of a triangle is 74°. One of its two interior opposite angles is 37°. What is the other one (in degrees)?

Answer key

  1. No
  2. No
  3. 84
  4. 68
  5. 45
  6. 25
  7. 72
  8. 72
  9. 112
  10. 80
  11. 20
  12. 8
  13. 57
  14. 52
  15. 101
  16. 17
  17. 36
  18. 23
  19. 70
  20. 14
  21. 15
  22. 59
  23. 81
  24. 30
  25. 99
  26. 64
  27. 90
  28. 72
  29. 10
  30. 65
  31. 48
  32. Yes
  33. 56
  34. 134
  35. 48
  36. 13
  37. 80
  38. 77
  39. 37
  40. 37

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