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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 233 · 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 triangle ABC, angle A = 51° and angle B = 79°. What is angle C (in degrees)?
  2. 2.The two interior opposite angles of a triangle are 31° and 29°. What is the exterior angle (in degrees)?
  3. 3.In triangle ABC, angle A = 60° and angle B = 23°. What is angle C (in degrees)?
  4. 4.An exterior angle of a triangle is 81°. One of its two interior opposite angles is 41°. What is the other one (in degrees)?
  5. 5.The two shorter sides of a right-angled triangle are 7 cm and 24 cm. How long is the longest side (in cm)?
  6. 6.The two shorter sides of a right-angled triangle are 15 cm and 8 cm. How long is the longest side (in cm)?
  7. 7.An exterior angle of a triangle is 127°. One of its two interior opposite angles is 59°. What is the other one (in degrees)?
  8. 8.The angles of a triangle are in the ratio 3 : 5 : 7. What is the biggest angle (in degrees)?
  9. 9.In a right-angled triangle, one of the other two angles is 18°. What is the third angle (in degrees)?
  10. 10.In an isosceles triangle, the two equal angles are 83° each. What is the third angle (in degrees)?
  11. 11.In a right-angled triangle, one of the other two angles is 30°. What is the third angle (in degrees)?
  12. 12.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)?
  13. 13.In triangle ABC, angle A = 33° and angle B = 111°. What is angle C (in degrees)?
  14. 14.In a right-angled triangle, one of the other two angles is 13°. What is the third angle (in degrees)?
  15. 15.The two shorter sides of a right-angled triangle are 24 cm and 7 cm. How long is the longest side (in cm)?
  16. 16.In triangle ABC, angle A = 24° and angle B = 36°. What is angle C (in degrees)?
  17. 17.In an isosceles triangle, the angle between the two equal sides is 52°. What is each of the other two angles (in degrees)?
  18. 18.The longest side of a right-angled triangle is 39 cm and one of the other sides is 36 cm. How long is the third side (in cm)?
  19. 19.In an isosceles triangle, the two equal angles are 23° each. What is the third angle (in degrees)?
  20. 20.In triangle ABC, angle A = 92° and angle B = 57°. What is angle C (in degrees)?
  21. 21.The two interior opposite angles of a triangle are 51° and 25°. What is the exterior angle (in degrees)?
  22. 22.The two interior opposite angles of a triangle are 62° and 34°. What is the exterior angle (in degrees)?
  23. 23.The angles of a triangle are in the ratio 2 : 3 : 5. What is the biggest angle (in degrees)?
  24. 24.In an isosceles triangle, the angle between the two equal sides is 78°. What is each of the other two angles (in degrees)?
  25. 25.In a right-angled triangle, one of the other two angles is 11°. What is the third angle (in degrees)?
  26. 26.An exterior angle of a triangle is 94°. One of its two interior opposite angles is 33°. What is the other one (in degrees)?
  27. 27.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)?
  28. 28.The angles of a triangle are in the ratio 1 : 2 : 6. What is the biggest angle (in degrees)?
  29. 29.In triangle ABC, angle A = 36° and angle B = 54°. What is angle C (in degrees)?
  30. 30.The angles of a triangle are in the ratio 1 : 4 : 5. What is the biggest angle (in degrees)?
  31. 31.In a right-angled triangle, one of the other two angles is 19°. What is the third angle (in degrees)?
  32. 32.The two interior opposite angles of a triangle are 21° and 23°. What is the exterior angle (in degrees)?
  33. 33.In an isosceles triangle, the angle between the two equal sides is 22°. What is each of the other two angles (in degrees)?
  34. 34.The angles of a triangle are in the ratio 1 : 3 : 5. What is the smallest angle (in degrees)?
  35. 35.An exterior angle of a triangle is 101°. One of its two interior opposite angles is 32°. What is the other one (in degrees)?
  36. 36.In an isosceles triangle, the angle between the two equal sides is 80°. What is each of the other two angles (in degrees)?
  37. 37.The two interior opposite angles of a triangle are 72° and 24°. What is the exterior angle (in degrees)?
  38. 38.The two shorter sides of a right-angled triangle are 15 cm and 36 cm. How long is the longest side (in cm)?
  39. 39.Can a triangle have sides of 9 cm, 3 cm and 3 cm? (a) Yes (b) No
  40. 40.An exterior angle of a triangle is 52°. One of its two interior opposite angles is 23°. What is the other one (in degrees)?

Answer key

  1. 50
  2. 60
  3. 97
  4. 40
  5. 25
  6. 17
  7. 68
  8. 84
  9. 72
  10. 14
  11. 60
  12. 16
  13. 36
  14. 77
  15. 25
  16. 120
  17. 64
  18. 15
  19. 134
  20. 31
  21. 76
  22. 96
  23. 90
  24. 51
  25. 79
  26. 61
  27. 8
  28. 120
  29. 90
  30. 90
  31. 71
  32. 44
  33. 79
  34. 20
  35. 69
  36. 50
  37. 96
  38. 39
  39. No
  40. 29

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