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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 525 · 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.

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  1. 1.The angles of a triangle are in the ratio 1 : 2 : 3. What is the smallest angle (in degrees)?
  2. 2.In triangle ABC, angle A = 61° and angle B = 70°. What is angle C (in degrees)?
  3. 3.In triangle ABC, angle A = 100° and angle B = 36°. What is angle C (in degrees)?
  4. 4.In a right-angled triangle, one of the other two angles is 79°. What is the third angle (in degrees)?
  5. 5.In an isosceles triangle, the two equal angles are 31° each. What is the third angle (in degrees)?
  6. 6.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)?
  7. 7.In triangle ABC, angle A = 31° and angle B = 76°. What is angle C (in degrees)?
  8. 8.In triangle ABC, angle A = 30° and angle B = 41°. What is angle C (in degrees)?
  9. 9.The longest side of a right-angled triangle is 10 cm and one of the other sides is 6 cm. How long is the third side (in cm)?
  10. 10.In a right-angled triangle, one of the other two angles is 18°. What is the third angle (in degrees)?
  11. 11.In triangle ABC, angle A = 38° and angle B = 45°. What is angle C (in degrees)?
  12. 12.Can a triangle have sides of 9 cm, 9 cm and 6 cm? (a) No (b) Yes
  13. 13.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)?
  14. 14.In triangle ABC, angle A = 42° and angle B = 43°. What is angle C (in degrees)?
  15. 15.In an isosceles triangle, the two equal angles are 32° each. What is the third angle (in degrees)?
  16. 16.The two interior opposite angles of a triangle are 61° and 72°. What is the exterior angle (in degrees)?
  17. 17.The two interior opposite angles of a triangle are 21° and 29°. What is the exterior angle (in degrees)?
  18. 18.In a right-angled triangle, one of the other two angles is 14°. What is the third angle (in degrees)?
  19. 19.Can a triangle have sides of 10 cm, 10 cm and 21 cm? (a) Yes (b) No
  20. 20.In an isosceles triangle, the two equal angles are 63° each. What is the third angle (in degrees)?
  21. 21.The two interior opposite angles of a triangle are 28° and 56°. What is the exterior angle (in degrees)?
  22. 22.In a right-angled triangle, one of the other two angles is 64°. What is the third angle (in degrees)?
  23. 23.In triangle ABC, angle A = 98° and angle B = 61°. What is angle C (in degrees)?
  24. 24.The two shorter sides of a right-angled triangle are 9 cm and 12 cm. How long is the longest side (in cm)?
  25. 25.In a right-angled triangle, one of the other two angles is 48°. What is the third angle (in degrees)?
  26. 26.In a right-angled triangle, one of the other two angles is 20°. What is the third angle (in degrees)?
  27. 27.Can a triangle have sides of 5 cm, 15 cm and 10 cm? (a) Yes (b) No
  28. 28.In triangle ABC, angle A = 28° and angle B = 20°. What is angle C (in degrees)?
  29. 29.In triangle ABC, angle A = 70° and angle B = 21°. What is angle C (in degrees)?
  30. 30.Can a triangle have sides of 2 cm, 6 cm and 5 cm? (a) Yes (b) No
  31. 31.In a right-angled triangle, one of the other two angles is 29°. What is the third angle (in degrees)?
  32. 32.An exterior angle of a triangle is 99°. One of its two interior opposite angles is 42°. What is the other one (in degrees)?
  33. 33.The two shorter sides of a right-angled triangle are 7 cm and 24 cm. How long is the longest side (in cm)?
  34. 34.The two shorter sides of a right-angled triangle are 20 cm and 15 cm. How long is the longest side (in cm)?
  35. 35.The two interior opposite angles of a triangle are 52° and 68°. What is the exterior angle (in degrees)?
  36. 36.The angles of a triangle are in the ratio 3 : 3 : 4. What is the biggest angle (in degrees)?
  37. 37.In an isosceles triangle, the angle between the two equal sides is 38°. What is each of the other two angles (in degrees)?
  38. 38.Can a triangle have sides of 10 cm, 2 cm and 10 cm? (a) Yes (b) No
  39. 39.The two shorter sides of a right-angled triangle are 24 cm and 7 cm. How long is the longest side (in cm)?
  40. 40.In triangle ABC, angle A = 23° and angle B = 48°. What is angle C (in degrees)?

Answer key

  1. 30
  2. 49
  3. 44
  4. 11
  5. 118
  6. 20
  7. 73
  8. 109
  9. 8
  10. 72
  11. 97
  12. Yes
  13. 8
  14. 95
  15. 116
  16. 133
  17. 50
  18. 76
  19. No
  20. 54
  21. 84
  22. 26
  23. 21
  24. 15
  25. 42
  26. 70
  27. No
  28. 132
  29. 89
  30. Yes
  31. 61
  32. 57
  33. 25
  34. 25
  35. 120
  36. 72
  37. 71
  38. Yes
  39. 25
  40. 109

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