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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 313 · 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 31°. What is the third angle (in degrees)?
  2. 2.In an isosceles triangle, the two equal angles are 84° each. What is the third angle (in degrees)?
  3. 3.In triangle ABC, angle A = 51° and angle B = 27°. What is angle C (in degrees)?
  4. 4.In an isosceles triangle, the angle between the two equal sides is 146°. What is each of the other two angles (in degrees)?
  5. 5.The two interior opposite angles of a triangle are 75° and 57°. What is the exterior angle (in degrees)?
  6. 6.The angles of a triangle are in the ratio 2 : 3 : 4. What is the biggest angle (in degrees)?
  7. 7.In triangle ABC, angle A = 73° and angle B = 24°. What is angle C (in degrees)?
  8. 8.Can a triangle have sides of 12 cm, 26 cm and 10 cm? (a) No (b) Yes
  9. 9.The two interior opposite angles of a triangle are 50° and 61°. What is the exterior angle (in degrees)?
  10. 10.Can a triangle have sides of 11 cm, 22 cm and 10 cm? (a) Yes (b) No
  11. 11.The angles of a triangle are in the ratio 1 : 3 : 5. What is the smallest angle (in degrees)?
  12. 12.Can a triangle have sides of 8 cm, 7 cm and 2 cm? (a) Yes (b) No
  13. 13.In an isosceles triangle, the angle between the two equal sides is 80°. What is each of the other two angles (in degrees)?
  14. 14.An exterior angle of a triangle is 49°. One of its two interior opposite angles is 26°. What is the other one (in degrees)?
  15. 15.In triangle ABC, angle A = 20° and angle B = 102°. What is angle C (in degrees)?
  16. 16.In triangle ABC, angle A = 37° and angle B = 94°. What is angle C (in degrees)?
  17. 17.In triangle ABC, angle A = 31° and angle B = 61°. What is angle C (in degrees)?
  18. 18.In an isosceles triangle, the two equal angles are 42° each. What is the third angle (in degrees)?
  19. 19.Can a triangle have sides of 5 cm, 18 cm and 12 cm? (a) Yes (b) No
  20. 20.The angles of a triangle are in the ratio 2 : 7 : 9. What is the biggest angle (in degrees)?
  21. 21.In triangle ABC, angle A = 40° and angle B = 61°. What is angle C (in degrees)?
  22. 22.The angles of a triangle are in the ratio 2 : 3 : 5. What is the biggest angle (in degrees)?
  23. 23.The angles of a triangle are in the ratio 1 : 2 : 6. What is the biggest angle (in degrees)?
  24. 24.The longest side of a right-angled triangle is 30 cm and one of the other sides is 24 cm. How long is the third side (in cm)?
  25. 25.In a right-angled triangle, one of the other two angles is 33°. What is the third angle (in degrees)?
  26. 26.In triangle ABC, angle A = 48° and angle B = 20°. What is angle C (in degrees)?
  27. 27.The angles of a triangle are in the ratio 4 : 5 : 6. What is the smallest angle (in degrees)?
  28. 28.In a right-angled triangle, one of the other two angles is 76°. What is the third angle (in degrees)?
  29. 29.An exterior angle of a triangle is 128°. One of its two interior opposite angles is 62°. What is the other one (in degrees)?
  30. 30.In a right-angled triangle, one of the other two angles is 11°. What is the third angle (in degrees)?
  31. 31.In a right-angled triangle, one of the other two angles is 67°. What is the third angle (in degrees)?
  32. 32.In triangle ABC, angle A = 64° and angle B = 73°. What is angle C (in degrees)?
  33. 33.The two interior opposite angles of a triangle are 32° and 38°. What is the exterior angle (in degrees)?
  34. 34.Can a triangle have sides of 4 cm, 8 cm and 4 cm? (a) Yes (b) No
  35. 35.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)?
  36. 36.In a right-angled triangle, one of the other two angles is 66°. What is the third angle (in degrees)?
  37. 37.Can a triangle have sides of 3 cm, 16 cm and 12 cm? (a) Yes (b) No
  38. 38.The two interior opposite angles of a triangle are 70° and 32°. What is the exterior angle (in degrees)?
  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.The two interior opposite angles of a triangle are 21° and 49°. What is the exterior angle (in degrees)?

Answer key

  1. 59
  2. 12
  3. 102
  4. 17
  5. 132
  6. 80
  7. 83
  8. No
  9. 111
  10. No
  11. 20
  12. Yes
  13. 50
  14. 23
  15. 58
  16. 49
  17. 88
  18. 96
  19. No
  20. 90
  21. 79
  22. 90
  23. 120
  24. 18
  25. 57
  26. 112
  27. 48
  28. 14
  29. 66
  30. 79
  31. 23
  32. 43
  33. 70
  34. No
  35. 24
  36. 24
  37. No
  38. 102
  39. 25
  40. 70

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