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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 63 · 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 angles of a triangle are in the ratio 2 : 3 : 5. What is the biggest angle (in degrees)?
  2. 2.The longest side of a right-angled triangle is 25 cm and one of the other sides is 15 cm. How long is the third side (in cm)?
  3. 3.Can a triangle have sides of 9 cm, 20 cm and 8 cm? (a) Yes (b) No
  4. 4.In an isosceles triangle, the two equal angles are 83° each. What is the third angle (in degrees)?
  5. 5.An exterior angle of a triangle is 100°. One of its two interior opposite angles is 72°. What is the other one (in degrees)?
  6. 6.In an isosceles triangle, the two equal angles are 38° each. What is the third angle (in degrees)?
  7. 7.In a right-angled triangle, one of the other two angles is 32°. What is the third angle (in degrees)?
  8. 8.In triangle ABC, angle A = 98° and angle B = 22°. What is angle C (in degrees)?
  9. 9.In triangle ABC, angle A = 85° and angle B = 55°. What is angle C (in degrees)?
  10. 10.In a right-angled triangle, one of the other two angles is 71°. What is the third angle (in degrees)?
  11. 11.The angles of a triangle are in the ratio 1 : 3 : 5. What is the smallest angle (in degrees)?
  12. 12.Can a triangle have sides of 9 cm, 11 cm and 25 cm? (a) No (b) Yes
  13. 13.In an isosceles triangle, the two equal angles are 82° each. What is the third angle (in degrees)?
  14. 14.An exterior angle of a triangle is 79°. One of its two interior opposite angles is 33°. What is the other one (in degrees)?
  15. 15.In triangle ABC, angle A = 99° and angle B = 36°. What is angle C (in degrees)?
  16. 16.In a right-angled triangle, one of the other two angles is 43°. What is the third angle (in degrees)?
  17. 17.An exterior angle of a triangle is 79°. One of its two interior opposite angles is 38°. What is the other one (in degrees)?
  18. 18.The two shorter sides of a right-angled triangle are 8 cm and 6 cm. How long is the longest side (in cm)?
  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 angle between the two equal sides is 130°. What is each of the other two angles (in degrees)?
  21. 21.In an isosceles triangle, the angle between the two equal sides is 142°. What is each of the other two angles (in degrees)?
  22. 22.Can a triangle have sides of 10 cm, 22 cm and 12 cm? (a) No (b) Yes
  23. 23.Can a triangle have sides of 7 cm, 8 cm and 2 cm? (a) No (b) Yes
  24. 24.In triangle ABC, angle A = 52° and angle B = 22°. What is angle C (in degrees)?
  25. 25.In an isosceles triangle, the two equal angles are 77° each. What is the third angle (in degrees)?
  26. 26.Can a triangle have sides of 21 cm, 12 cm and 10 cm? (a) Yes (b) No
  27. 27.The two shorter sides of a right-angled triangle are 15 cm and 36 cm. How long is the longest side (in cm)?
  28. 28.The two interior opposite angles of a triangle are 37° and 22°. What is the exterior angle (in degrees)?
  29. 29.An exterior angle of a triangle is 107°. One of its two interior opposite angles is 36°. What is the other one (in degrees)?
  30. 30.Can a triangle have sides of 7 cm, 6 cm and 9 cm? (a) No (b) Yes
  31. 31.An exterior angle of a triangle is 115°. One of its two interior opposite angles is 65°. What is the other one (in degrees)?
  32. 32.The angles of a triangle are in the ratio 4 : 5 : 6. What is the biggest angle (in degrees)?
  33. 33.The longest side of a right-angled triangle is 30 cm and one of the other sides is 18 cm. How long is the third side (in cm)?
  34. 34.In a right-angled triangle, one of the other two angles is 15°. What is the third angle (in degrees)?
  35. 35.The two interior opposite angles of a triangle are 53° and 70°. What is the exterior angle (in degrees)?
  36. 36.In triangle ABC, angle A = 42° and angle B = 65°. What is angle C (in degrees)?
  37. 37.The two shorter sides of a right-angled triangle are 8 cm and 15 cm. How long is the longest side (in cm)?
  38. 38.In triangle ABC, angle A = 93° and angle B = 24°. What is angle C (in degrees)?
  39. 39.The angles of a triangle are in the ratio 3 : 3 : 4. What is the biggest angle (in degrees)?
  40. 40.In a right-angled triangle, one of the other two angles is 36°. What is the third angle (in degrees)?

Answer key

  1. 90
  2. 20
  3. No
  4. 14
  5. 28
  6. 104
  7. 58
  8. 60
  9. 40
  10. 19
  11. 20
  12. No
  13. 16
  14. 46
  15. 45
  16. 47
  17. 41
  18. 10
  19. 70
  20. 25
  21. 19
  22. No
  23. Yes
  24. 106
  25. 26
  26. Yes
  27. 39
  28. 59
  29. 71
  30. Yes
  31. 50
  32. 72
  33. 24
  34. 75
  35. 123
  36. 73
  37. 17
  38. 63
  39. 72
  40. 54

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