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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 644 · 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.

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  1. 1.In an isosceles triangle, the two equal angles are 58° each. What is the third angle (in degrees)?
  2. 2.Can a triangle have sides of 6 cm, 18 cm and 10 cm? (a) No (b) Yes
  3. 3.In a right-angled triangle, one of the other two angles is 74°. What is the third angle (in degrees)?
  4. 4.Can a triangle have sides of 4 cm, 16 cm and 12 cm? (a) Yes (b) No
  5. 5.An exterior angle of a triangle is 77°. One of its two interior opposite angles is 54°. What is the other one (in degrees)?
  6. 6.Can a triangle have sides of 20 cm, 8 cm and 8 cm? (a) Yes (b) No
  7. 7.In a right-angled triangle, one of the other two angles is 72°. What is the third angle (in degrees)?
  8. 8.In triangle ABC, angle A = 90° and angle B = 61°. What is angle C (in degrees)?
  9. 9.Can a triangle have sides of 3 cm, 11 cm and 18 cm? (a) Yes (b) No
  10. 10.The two interior opposite angles of a triangle are 78° and 23°. What is the exterior angle (in degrees)?
  11. 11.The two interior opposite angles of a triangle are 77° and 70°. What is the exterior angle (in degrees)?
  12. 12.In triangle ABC, angle A = 93° and angle B = 65°. What is angle C (in degrees)?
  13. 13.Can a triangle have sides of 7 cm, 10 cm and 3 cm? (a) No (b) Yes
  14. 14.In an isosceles triangle, the angle between the two equal sides is 34°. What is each of the other two angles (in degrees)?
  15. 15.In an isosceles triangle, the two equal angles are 23° each. What is the third angle (in degrees)?
  16. 16.In an isosceles triangle, the two equal angles are 79° each. What is the third angle (in degrees)?
  17. 17.In triangle ABC, angle A = 40° and angle B = 76°. What is angle C (in degrees)?
  18. 18.Can a triangle have sides of 4 cm, 7 cm and 13 cm? (a) No (b) Yes
  19. 19.In a right-angled triangle, one of the other two angles is 10°. What is the third angle (in degrees)?
  20. 20.The angles of a triangle are in the ratio 1 : 2 : 2. What is the biggest angle (in degrees)?
  21. 21.In a right-angled triangle, one of the other two angles is 21°. What is the third angle (in degrees)?
  22. 22.The two shorter sides of a right-angled triangle are 15 cm and 8 cm. How long is the longest side (in cm)?
  23. 23.The angles of a triangle are in the ratio 4 : 5 : 6. What is the smallest angle (in degrees)?
  24. 24.The angles of a triangle are in the ratio 2 : 2 : 5. What is the biggest angle (in degrees)?
  25. 25.The longest side of a right-angled triangle is 25 cm and one of the other sides is 24 cm. How long is the third side (in cm)?
  26. 26.The two interior opposite angles of a triangle are 22° and 69°. What is the exterior angle (in degrees)?
  27. 27.In an isosceles triangle, the angle between the two equal sides is 144°. What is each of the other two angles (in degrees)?
  28. 28.The angles of a triangle are in the ratio 5 : 6 : 7. What is the smallest angle (in degrees)?
  29. 29.In triangle ABC, angle A = 52° and angle B = 42°. What is angle C (in degrees)?
  30. 30.In triangle ABC, angle A = 42° and angle B = 99°. What is angle C (in degrees)?
  31. 31.In triangle ABC, angle A = 66° and angle B = 52°. What is angle C (in degrees)?
  32. 32.The angles of a triangle are in the ratio 2 : 7 : 9. What is the biggest angle (in degrees)?
  33. 33.Can a triangle have sides of 3 cm, 5 cm and 8 cm? (a) No (b) Yes
  34. 34.An exterior angle of a triangle is 74°. One of its two interior opposite angles is 28°. What is the other one (in degrees)?
  35. 35.In triangle ABC, angle A = 53° and angle B = 48°. What is angle C (in degrees)?
  36. 36.The two interior opposite angles of a triangle are 21° and 68°. What is the exterior angle (in degrees)?
  37. 37.Can a triangle have sides of 6 cm, 7 cm and 9 cm? (a) No (b) Yes
  38. 38.In an isosceles triangle, the angle between the two equal sides is 94°. What is each of the other two angles (in degrees)?
  39. 39.In triangle ABC, angle A = 67° and angle B = 72°. What is angle C (in degrees)?
  40. 40.The two interior opposite angles of a triangle are 58° and 62°. What is the exterior angle (in degrees)?

Answer key

  1. 64
  2. No
  3. 16
  4. No
  5. 23
  6. No
  7. 18
  8. 29
  9. No
  10. 101
  11. 147
  12. 22
  13. No
  14. 73
  15. 134
  16. 22
  17. 64
  18. No
  19. 80
  20. 72
  21. 69
  22. 17
  23. 48
  24. 100
  25. 7
  26. 91
  27. 18
  28. 50
  29. 86
  30. 39
  31. 62
  32. 90
  33. No
  34. 46
  35. 79
  36. 89
  37. Yes
  38. 43
  39. 41
  40. 120

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