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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 794 · 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 a right-angled triangle, one of the other two angles is 14°. What is the third angle (in degrees)?
  2. 2.In an isosceles triangle, the angle between the two equal sides is 38°. What is each of the other two angles (in degrees)?
  3. 3.An exterior angle of a triangle is 138°. One of its two interior opposite angles is 63°. What is the other one (in degrees)?
  4. 4.The two shorter sides of a right-angled triangle are 9 cm and 12 cm. How long is the longest side (in cm)?
  5. 5.Can a triangle have sides of 17 cm, 7 cm and 7 cm? (a) No (b) Yes
  6. 6.An exterior angle of a triangle is 71°. One of its two interior opposite angles is 40°. What is the other one (in degrees)?
  7. 7.Can a triangle have sides of 5 cm, 12 cm and 8 cm? (a) Yes (b) No
  8. 8.In triangle ABC, angle A = 66° and angle B = 75°. What is angle C (in degrees)?
  9. 9.In triangle ABC, angle A = 26° and angle B = 20°. What is angle C (in degrees)?
  10. 10.In triangle ABC, angle A = 33° and angle B = 32°. What is angle C (in degrees)?
  11. 11.An exterior angle of a triangle is 90°. One of its two interior opposite angles is 34°. What is the other one (in degrees)?
  12. 12.The angles of a triangle are in the ratio 1 : 2 : 6. What is the biggest angle (in degrees)?
  13. 13.In triangle ABC, angle A = 88° and angle B = 23°. What is angle C (in degrees)?
  14. 14.In triangle ABC, angle A = 26° and angle B = 133°. What is angle C (in degrees)?
  15. 15.Can a triangle have sides of 7 cm, 13 cm and 7 cm? (a) Yes (b) No
  16. 16.The longest side of a right-angled triangle is 20 cm and one of the other sides is 12 cm. How long is the third side (in cm)?
  17. 17.The two interior opposite angles of a triangle are 80° and 37°. What is the exterior angle (in degrees)?
  18. 18.In an isosceles triangle, the angle between the two equal sides is 70°. What is each of the other two angles (in degrees)?
  19. 19.In a right-angled triangle, one of the other two angles is 68°. What is the third angle (in degrees)?
  20. 20.In triangle ABC, angle A = 70° and angle B = 69°. What is angle C (in degrees)?
  21. 21.In a right-angled triangle, one of the other two angles is 77°. What is the third angle (in degrees)?
  22. 22.Can a triangle have sides of 4 cm, 7 cm and 7 cm? (a) No (b) Yes
  23. 23.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)?
  24. 24.The two interior opposite angles of a triangle are 70° and 36°. What is the exterior angle (in degrees)?
  25. 25.In an isosceles triangle, the two equal angles are 50° each. What is the third angle (in degrees)?
  26. 26.The two interior opposite angles of a triangle are 51° and 58°. What is the exterior angle (in degrees)?
  27. 27.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)?
  28. 28.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)?
  29. 29.In an isosceles triangle, the angle between the two equal sides is 98°. What is each of the other two angles (in degrees)?
  30. 30.In a right-angled triangle, one of the other two angles is 79°. What is the third angle (in degrees)?
  31. 31.In an isosceles triangle, the angle between the two equal sides is 32°. What is each of the other two angles (in degrees)?
  32. 32.In a right-angled triangle, one of the other two angles is 67°. What is the third angle (in degrees)?
  33. 33.An exterior angle of a triangle is 133°. One of its two interior opposite angles is 59°. What is the other one (in degrees)?
  34. 34.The angles of a triangle are in the ratio 1 : 2 : 3. What is the biggest angle (in degrees)?
  35. 35.Can a triangle have sides of 8 cm, 7 cm and 10 cm? (a) No (b) Yes
  36. 36.Can a triangle have sides of 11 cm, 11 cm and 10 cm? (a) Yes (b) No
  37. 37.The angles of a triangle are in the ratio 1 : 1 : 2. What is the biggest angle (in degrees)?
  38. 38.In triangle ABC, angle A = 49° and angle B = 101°. What is angle C (in degrees)?
  39. 39.The angles of a triangle are in the ratio 4 : 5 : 6. What is the biggest angle (in degrees)?
  40. 40.The two interior opposite angles of a triangle are 58° and 29°. What is the exterior angle (in degrees)?

Answer key

  1. 76
  2. 71
  3. 75
  4. 15
  5. No
  6. 31
  7. Yes
  8. 39
  9. 134
  10. 115
  11. 56
  12. 120
  13. 69
  14. 21
  15. Yes
  16. 16
  17. 117
  18. 55
  19. 22
  20. 41
  21. 13
  22. Yes
  23. 15
  24. 106
  25. 80
  26. 109
  27. 7
  28. 24
  29. 41
  30. 11
  31. 74
  32. 23
  33. 74
  34. 90
  35. Yes
  36. Yes
  37. 90
  38. 30
  39. 72
  40. 87

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