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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 309 · 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.In a right-angled triangle, one of the other two angles is 51°. What is the third angle (in degrees)?
  2. 2.In a right-angled triangle, one of the other two angles is 74°. What is the third angle (in degrees)?
  3. 3.In a right-angled triangle, one of the other two angles is 23°. What is the third angle (in degrees)?
  4. 4.The angles of a triangle are in the ratio 3 : 3 : 4. What is the biggest angle (in degrees)?
  5. 5.The angles of a triangle are in the ratio 3 : 4 : 5. What is the smallest angle (in degrees)?
  6. 6.The angles of a triangle are in the ratio 1 : 2 : 6. What is the biggest angle (in degrees)?
  7. 7.The angles of a triangle are in the ratio 1 : 1 : 2. What is the smallest angle (in degrees)?
  8. 8.The angles of a triangle are in the ratio 5 : 6 : 7. What is the biggest angle (in degrees)?
  9. 9.In triangle ABC, angle A = 43° and angle B = 96°. What is angle C (in degrees)?
  10. 10.The angles of a triangle are in the ratio 2 : 3 : 4. What is the biggest angle (in degrees)?
  11. 11.The two interior opposite angles of a triangle are 31° and 30°. What is the exterior angle (in degrees)?
  12. 12.In an isosceles triangle, the two equal angles are 54° each. What is the third angle (in degrees)?
  13. 13.In triangle ABC, angle A = 88° and angle B = 42°. What is angle C (in degrees)?
  14. 14.In triangle ABC, angle A = 39° and angle B = 40°. What is angle C (in degrees)?
  15. 15.In triangle ABC, angle A = 89° and angle B = 33°. What is angle C (in degrees)?
  16. 16.In an isosceles triangle, the two equal angles are 35° each. What is the third angle (in degrees)?
  17. 17.In a right-angled triangle, one of the other two angles is 12°. What is the third angle (in degrees)?
  18. 18.The angles of a triangle are in the ratio 1 : 3 : 5. What is the biggest angle (in degrees)?
  19. 19.An exterior angle of a triangle is 60°. One of its two interior opposite angles is 37°. What is the other one (in degrees)?
  20. 20.In triangle ABC, angle A = 24° and angle B = 86°. What is angle C (in degrees)?
  21. 21.In a right-angled triangle, one of the other two angles is 20°. What is the third angle (in degrees)?
  22. 22.In triangle ABC, angle A = 70° and angle B = 23°. What is angle C (in degrees)?
  23. 23.The angles of a triangle are in the ratio 3 : 3 : 4. What is the smallest angle (in degrees)?
  24. 24.The angles of a triangle are in the ratio 1 : 1 : 2. What is the biggest angle (in degrees)?
  25. 25.The angles of a triangle are in the ratio 5 : 6 : 7. What is the smallest angle (in degrees)?
  26. 26.The angles of a triangle are in the ratio 1 : 2 : 6. What is the smallest angle (in degrees)?
  27. 27.The longest side of a right-angled triangle is 39 cm and one of the other sides is 15 cm. How long is the third side (in cm)?
  28. 28.In a right-angled triangle, one of the other two angles is 54°. What is the third angle (in degrees)?
  29. 29.In a right-angled triangle, one of the other two angles is 25°. What is the third angle (in degrees)?
  30. 30.In an isosceles triangle, the angle between the two equal sides is 94°. What is each of the other two angles (in degrees)?
  31. 31.An exterior angle of a triangle is 94°. One of its two interior opposite angles is 57°. What is the other one (in degrees)?
  32. 32.Can a triangle have sides of 10 cm, 10 cm and 9 cm? (a) Yes (b) No
  33. 33.The two shorter sides of a right-angled triangle are 15 cm and 8 cm. How long is the longest side (in cm)?
  34. 34.An exterior angle of a triangle is 80°. One of its two interior opposite angles is 54°. What is the other one (in degrees)?
  35. 35.In a right-angled triangle, one of the other two angles is 35°. What is the third angle (in degrees)?
  36. 36.In a right-angled triangle, one of the other two angles is 57°. What is the third angle (in degrees)?
  37. 37.In a right-angled triangle, one of the other two angles is 13°. What is the third angle (in degrees)?
  38. 38.Can a triangle have sides of 4 cm, 15 cm and 10 cm? (a) No (b) Yes
  39. 39.The two shorter sides of a right-angled triangle are 5 cm and 12 cm. How long is the longest side (in cm)?
  40. 40.An exterior angle of a triangle is 105°. One of its two interior opposite angles is 52°. What is the other one (in degrees)?

Answer key

  1. 39
  2. 16
  3. 67
  4. 72
  5. 45
  6. 120
  7. 45
  8. 70
  9. 41
  10. 80
  11. 61
  12. 72
  13. 50
  14. 101
  15. 58
  16. 110
  17. 78
  18. 100
  19. 23
  20. 70
  21. 70
  22. 87
  23. 54
  24. 90
  25. 50
  26. 20
  27. 36
  28. 36
  29. 65
  30. 43
  31. 37
  32. Yes
  33. 17
  34. 26
  35. 55
  36. 33
  37. 77
  38. No
  39. 13
  40. 53

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