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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 138 · 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.The longest side of a right-angled triangle is 20 cm and one of the other sides is 16 cm. How long is the third side (in cm)?
  2. 2.In a right-angled triangle, one of the other two angles is 27°. What is the third angle (in degrees)?
  3. 3.In a right-angled triangle, one of the other two angles is 68°. What is the third angle (in degrees)?
  4. 4.In an isosceles triangle, the two equal angles are 81° each. What is the third angle (in degrees)?
  5. 5.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)?
  6. 6.Can a triangle have sides of 7 cm, 18 cm and 11 cm? (a) Yes (b) No
  7. 7.In a right-angled triangle, one of the other two angles is 36°. What is the third angle (in degrees)?
  8. 8.Can a triangle have sides of 5 cm, 6 cm and 2 cm? (a) No (b) Yes
  9. 9.Can a triangle have sides of 3 cm, 7 cm and 7 cm? (a) No (b) Yes
  10. 10.In triangle ABC, angle A = 87° and angle B = 61°. What is angle C (in degrees)?
  11. 11.In triangle ABC, angle A = 84° and angle B = 25°. What is angle C (in degrees)?
  12. 12.The longest side of a right-angled triangle is 10 cm and one of the other sides is 8 cm. How long is the third side (in cm)?
  13. 13.In triangle ABC, angle A = 82° and angle B = 32°. What is angle C (in degrees)?
  14. 14.In an isosceles triangle, the two equal angles are 40° each. What is the third angle (in degrees)?
  15. 15.In triangle ABC, angle A = 92° and angle B = 22°. What is angle C (in degrees)?
  16. 16.In triangle ABC, angle A = 63° and angle B = 87°. What is angle C (in degrees)?
  17. 17.The longest side of a right-angled triangle is 15 cm and one of the other sides is 12 cm. How long is the third side (in cm)?
  18. 18.In a right-angled triangle, one of the other two angles is 38°. What is the third angle (in degrees)?
  19. 19.In a right-angled triangle, one of the other two angles is 32°. What is the third angle (in degrees)?
  20. 20.An exterior angle of a triangle is 98°. One of its two interior opposite angles is 66°. What is the other one (in degrees)?
  21. 21.In triangle ABC, angle A = 60° and angle B = 33°. What is angle C (in degrees)?
  22. 22.Can a triangle have sides of 14 cm, 5 cm and 5 cm? (a) No (b) Yes
  23. 23.The angles of a triangle are in the ratio 1 : 2 : 3. What is the smallest angle (in degrees)?
  24. 24.In an isosceles triangle, the angle between the two equal sides is 146°. What is each of the other two angles (in degrees)?
  25. 25.In triangle ABC, angle A = 62° and angle B = 93°. What is angle C (in degrees)?
  26. 26.The angles of a triangle are in the ratio 1 : 2 : 3. What is the biggest angle (in degrees)?
  27. 27.The two shorter sides of a right-angled triangle are 7 cm and 24 cm. How long is the longest side (in cm)?
  28. 28.In a right-angled triangle, one of the other two angles is 69°. What is the third angle (in degrees)?
  29. 29.In an isosceles triangle, the angle between the two equal sides is 46°. What is each of the other two angles (in degrees)?
  30. 30.An exterior angle of a triangle is 61°. One of its two interior opposite angles is 26°. What is the other one (in degrees)?
  31. 31.In a right-angled triangle, one of the other two angles is 60°. What is the third angle (in degrees)?
  32. 32.An exterior angle of a triangle is 105°. One of its two interior opposite angles is 39°. What is the other one (in degrees)?
  33. 33.In a right-angled triangle, one of the other two angles is 13°. What is the third angle (in degrees)?
  34. 34.Can a triangle have sides of 8 cm, 9 cm and 17 cm? (a) No (b) Yes
  35. 35.The two interior opposite angles of a triangle are 29° and 30°. What is the exterior angle (in degrees)?
  36. 36.In triangle ABC, angle A = 57° and angle B = 81°. What is angle C (in degrees)?
  37. 37.Can a triangle have sides of 12 cm, 20 cm and 4 cm? (a) Yes (b) No
  38. 38.Can a triangle have sides of 4 cm, 11 cm and 5 cm? (a) Yes (b) No
  39. 39.In triangle ABC, angle A = 69° and angle B = 36°. What is angle C (in degrees)?
  40. 40.The angles of a triangle are in the ratio 2 : 2 : 5. What is the biggest angle (in degrees)?

Answer key

  1. 12
  2. 63
  3. 22
  4. 18
  5. 24
  6. No
  7. 54
  8. Yes
  9. Yes
  10. 32
  11. 71
  12. 6
  13. 66
  14. 100
  15. 66
  16. 30
  17. 9
  18. 52
  19. 58
  20. 32
  21. 87
  22. No
  23. 30
  24. 17
  25. 25
  26. 90
  27. 25
  28. 21
  29. 67
  30. 35
  31. 30
  32. 66
  33. 77
  34. No
  35. 59
  36. 42
  37. No
  38. No
  39. 75
  40. 100

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