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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 370 · 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 5 cm, 12 cm and 9 cm? (a) No (b) Yes
  2. 2.An exterior angle of a triangle is 128°. One of its two interior opposite angles is 58°. What is the other one (in degrees)?
  3. 3.An exterior angle of a triangle is 101°. One of its two interior opposite angles is 65°. What is the other one (in degrees)?
  4. 4.In an isosceles triangle, the angle between the two equal sides is 26°. What is each of the other two angles (in degrees)?
  5. 5.In an isosceles triangle, the two equal angles are 72° each. What is the third angle (in degrees)?
  6. 6.In an isosceles triangle, the angle between the two equal sides is 98°. What is each of the other two angles (in degrees)?
  7. 7.An exterior angle of a triangle is 94°. One of its two interior opposite angles is 25°. What is the other one (in degrees)?
  8. 8.An exterior angle of a triangle is 129°. One of its two interior opposite angles is 64°. What is the other one (in degrees)?
  9. 9.The two interior opposite angles of a triangle are 40° and 77°. What is the exterior angle (in degrees)?
  10. 10.Can a triangle have sides of 4 cm, 7 cm and 7 cm? (a) Yes (b) No
  11. 11.Can a triangle have sides of 11 cm, 11 cm and 3 cm? (a) Yes (b) No
  12. 12.In triangle ABC, angle A = 89° and angle B = 59°. What is angle C (in degrees)?
  13. 13.An exterior angle of a triangle is 107°. One of its two interior opposite angles is 66°. What is the other one (in degrees)?
  14. 14.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)?
  15. 15.The angles of a triangle are in the ratio 1 : 3 : 5. What is the smallest angle (in degrees)?
  16. 16.The angles of a triangle are in the ratio 1 : 1 : 2. What is the biggest angle (in degrees)?
  17. 17.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)?
  18. 18.In a right-angled triangle, one of the other two angles is 43°. What is the third angle (in degrees)?
  19. 19.Can a triangle have sides of 9 cm, 5 cm and 5 cm? (a) Yes (b) No
  20. 20.In triangle ABC, angle A = 30° and angle B = 65°. What is angle C (in degrees)?
  21. 21.The angles of a triangle are in the ratio 4 : 5 : 6. What is the biggest angle (in degrees)?
  22. 22.In a right-angled triangle, one of the other two angles is 21°. What is the third angle (in degrees)?
  23. 23.The two interior opposite angles of a triangle are 40° and 63°. What is the exterior angle (in degrees)?
  24. 24.An exterior angle of a triangle is 67°. One of its two interior opposite angles is 40°. What is the other one (in degrees)?
  25. 25.In a right-angled triangle, one of the other two angles is 25°. What is the third angle (in degrees)?
  26. 26.In a right-angled triangle, one of the other two angles is 38°. What is the third angle (in degrees)?
  27. 27.In a right-angled triangle, one of the other two angles is 67°. What is the third angle (in degrees)?
  28. 28.The angles of a triangle are in the ratio 1 : 1 : 2. What is the smallest angle (in degrees)?
  29. 29.In an isosceles triangle, the two equal angles are 32° each. What is the third angle (in degrees)?
  30. 30.The angles of a triangle are in the ratio 1 : 2 : 6. What is the smallest angle (in degrees)?
  31. 31.In triangle ABC, angle A = 48° and angle B = 101°. What is angle C (in degrees)?
  32. 32.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)?
  33. 33.In triangle ABC, angle A = 62° and angle B = 28°. What is angle C (in degrees)?
  34. 34.In an isosceles triangle, the angle between the two equal sides is 120°. What is each of the other two angles (in degrees)?
  35. 35.Can a triangle have sides of 10 cm, 19 cm and 5 cm? (a) No (b) Yes
  36. 36.In triangle ABC, angle A = 76° and angle B = 69°. What is angle C (in degrees)?
  37. 37.In an isosceles triangle, the angle between the two equal sides is 146°. What is each of the other two angles (in degrees)?
  38. 38.In a right-angled triangle, one of the other two angles is 78°. What is the third angle (in degrees)?
  39. 39.Can a triangle have sides of 3 cm, 12 cm and 12 cm? (a) No (b) Yes
  40. 40.In triangle ABC, angle A = 21° and angle B = 106°. What is angle C (in degrees)?

Answer key

  1. Yes
  2. 70
  3. 36
  4. 77
  5. 36
  6. 41
  7. 69
  8. 65
  9. 117
  10. Yes
  11. Yes
  12. 32
  13. 41
  14. 15
  15. 20
  16. 90
  17. 24
  18. 47
  19. Yes
  20. 85
  21. 72
  22. 69
  23. 103
  24. 27
  25. 65
  26. 52
  27. 23
  28. 45
  29. 116
  30. 20
  31. 31
  32. 8
  33. 90
  34. 30
  35. No
  36. 35
  37. 17
  38. 12
  39. Yes
  40. 53

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