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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 366 · 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 1 : 2 : 6. What is the biggest angle (in degrees)?
  2. 2.The angles of a triangle are in the ratio 3 : 3 : 4. What is the biggest angle (in degrees)?
  3. 3.In triangle ABC, angle A = 25° and angle B = 83°. What is angle C (in degrees)?
  4. 4.An exterior angle of a triangle is 64°. One of its two interior opposite angles is 44°. What is the other one (in degrees)?
  5. 5.An exterior angle of a triangle is 151°. One of its two interior opposite angles is 80°. What is the other one (in degrees)?
  6. 6.An exterior angle of a triangle is 137°. One of its two interior opposite angles is 63°. What is the other one (in degrees)?
  7. 7.Can a triangle have sides of 11 cm, 12 cm and 9 cm? (a) No (b) Yes
  8. 8.In triangle ABC, angle A = 72° and angle B = 31°. What is angle C (in degrees)?
  9. 9.An exterior angle of a triangle is 139°. One of its two interior opposite angles is 78°. What is the other one (in degrees)?
  10. 10.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)?
  11. 11.Can a triangle have sides of 9 cm, 5 cm and 14 cm? (a) Yes (b) No
  12. 12.Can a triangle have sides of 2 cm, 6 cm and 7 cm? (a) No (b) Yes
  13. 13.The two shorter sides of a right-angled triangle are 15 cm and 36 cm. How long is the longest side (in cm)?
  14. 14.An exterior angle of a triangle is 98°. One of its two interior opposite angles is 23°. What is the other one (in degrees)?
  15. 15.An exterior angle of a triangle is 102°. One of its two interior opposite angles is 28°. What is the other one (in degrees)?
  16. 16.In triangle ABC, angle A = 86° and angle B = 43°. What is angle C (in degrees)?
  17. 17.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)?
  18. 18.In an isosceles triangle, the two equal angles are 85° each. What is the third angle (in degrees)?
  19. 19.Can a triangle have sides of 10 cm, 16 cm and 10 cm? (a) Yes (b) No
  20. 20.In triangle ABC, angle A = 50° and angle B = 84°. What is angle C (in degrees)?
  21. 21.In an isosceles triangle, the two equal angles are 20° each. What is the third angle (in degrees)?
  22. 22.In an isosceles triangle, the two equal angles are 77° each. What is the third angle (in degrees)?
  23. 23.In an isosceles triangle, the angle between the two equal sides is 146°. What is each of the other two angles (in degrees)?
  24. 24.Can a triangle have sides of 6 cm, 6 cm and 9 cm? (a) No (b) Yes
  25. 25.The two interior opposite angles of a triangle are 64° and 56°. What is the exterior angle (in degrees)?
  26. 26.An exterior angle of a triangle is 85°. One of its two interior opposite angles is 56°. What is the other one (in degrees)?
  27. 27.In triangle ABC, angle A = 42° and angle B = 76°. What is angle C (in degrees)?
  28. 28.The two interior opposite angles of a triangle are 44° and 68°. What is the exterior angle (in degrees)?
  29. 29.In triangle ABC, angle A = 21° and angle B = 79°. What is angle C (in degrees)?
  30. 30.In an isosceles triangle, the two equal angles are 38° each. What is the third angle (in degrees)?
  31. 31.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)?
  32. 32.An exterior angle of a triangle is 92°. One of its two interior opposite angles is 47°. What is the other one (in degrees)?
  33. 33.Can a triangle have sides of 10 cm, 20 cm and 7 cm? (a) Yes (b) No
  34. 34.The angles of a triangle are in the ratio 5 : 6 : 7. What is the smallest angle (in degrees)?
  35. 35.The two interior opposite angles of a triangle are 34° and 51°. What is the exterior angle (in degrees)?
  36. 36.In triangle ABC, angle A = 76° and angle B = 60°. What is angle C (in degrees)?
  37. 37.In triangle ABC, angle A = 90° and angle B = 59°. What is angle C (in degrees)?
  38. 38.In an isosceles triangle, the angle between the two equal sides is 46°. What is each of the other two angles (in degrees)?
  39. 39.Can a triangle have sides of 8 cm, 8 cm and 18 cm? (a) Yes (b) No
  40. 40.In an isosceles triangle, the two equal angles are 84° each. What is the third angle (in degrees)?

Answer key

  1. 120
  2. 72
  3. 72
  4. 20
  5. 71
  6. 74
  7. Yes
  8. 77
  9. 61
  10. 24
  11. No
  12. Yes
  13. 39
  14. 75
  15. 74
  16. 51
  17. 15
  18. 10
  19. Yes
  20. 46
  21. 140
  22. 26
  23. 17
  24. Yes
  25. 120
  26. 29
  27. 62
  28. 112
  29. 80
  30. 104
  31. 8
  32. 45
  33. No
  34. 50
  35. 85
  36. 44
  37. 31
  38. 67
  39. No
  40. 12

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