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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 657 · 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.

NameDateTime takenScore ___ / 40
  1. 1.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)?
  2. 2.In triangle ABC, angle A = 100° and angle B = 20°. What is angle C (in degrees)?
  3. 3.Can a triangle have sides of 12 cm, 16 cm and 2 cm? (a) Yes (b) No
  4. 4.The two interior opposite angles of a triangle are 59° and 74°. What is the exterior angle (in degrees)?
  5. 5.In an isosceles triangle, the angle between the two equal sides is 84°. What is each of the other two angles (in degrees)?
  6. 6.In triangle ABC, angle A = 78° and angle B = 24°. What is angle C (in degrees)?
  7. 7.Can a triangle have sides of 12 cm, 2 cm and 10 cm? (a) No (b) Yes
  8. 8.The angles of a triangle are in the ratio 1 : 2 : 6. What is the smallest angle (in degrees)?
  9. 9.Can a triangle have sides of 6 cm, 11 cm and 7 cm? (a) No (b) Yes
  10. 10.In a right-angled triangle, one of the other two angles is 32°. What is the third angle (in degrees)?
  11. 11.In an isosceles triangle, the angle between the two equal sides is 20°. What is each of the other two angles (in degrees)?
  12. 12.The angles of a triangle are in the ratio 2 : 2 : 5. What is the smallest angle (in degrees)?
  13. 13.In an isosceles triangle, the angle between the two equal sides is 82°. What is each of the other two angles (in degrees)?
  14. 14.Can a triangle have sides of 9 cm, 11 cm and 23 cm? (a) No (b) Yes
  15. 15.Can a triangle have sides of 25 cm, 11 cm and 9 cm? (a) Yes (b) No
  16. 16.In an isosceles triangle, the two equal angles are 66° each. What is the third angle (in degrees)?
  17. 17.The two interior opposite angles of a triangle are 33° and 50°. What is the exterior angle (in degrees)?
  18. 18.In an isosceles triangle, the two equal angles are 24° each. What is the third angle (in degrees)?
  19. 19.An exterior angle of a triangle is 108°. One of its two interior opposite angles is 39°. What is the other one (in degrees)?
  20. 20.The two shorter sides of a right-angled triangle are 24 cm and 7 cm. How long is the longest side (in cm)?
  21. 21.The angles of a triangle are in the ratio 2 : 7 : 9. What is the smallest angle (in degrees)?
  22. 22.The angles of a triangle are in the ratio 1 : 3 : 5. What is the biggest angle (in degrees)?
  23. 23.The longest side of a right-angled triangle is 5 cm and one of the other sides is 4 cm. How long is the third side (in cm)?
  24. 24.An exterior angle of a triangle is 111°. One of its two interior opposite angles is 80°. What is the other one (in degrees)?
  25. 25.In triangle ABC, angle A = 57° and angle B = 69°. What is angle C (in degrees)?
  26. 26.In triangle ABC, angle A = 82° and angle B = 27°. What is angle C (in degrees)?
  27. 27.In an isosceles triangle, the two equal angles are 37° each. What is the third angle (in degrees)?
  28. 28.In triangle ABC, angle A = 58° and angle B = 55°. What is angle C (in degrees)?
  29. 29.The angles of a triangle are in the ratio 1 : 4 : 5. What is the smallest angle (in degrees)?
  30. 30.In a right-angled triangle, one of the other two angles is 41°. What is the third angle (in degrees)?
  31. 31.Can a triangle have sides of 23 cm, 8 cm and 12 cm? (a) Yes (b) No
  32. 32.The longest side of a right-angled triangle is 15 cm and one of the other sides is 9 cm. How long is the third side (in cm)?
  33. 33.In a right-angled triangle, one of the other two angles is 30°. What is the third angle (in degrees)?
  34. 34.In triangle ABC, angle A = 100° and angle B = 59°. What is angle C (in degrees)?
  35. 35.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)?
  36. 36.In an isosceles triangle, the two equal angles are 64° each. What is the third angle (in degrees)?
  37. 37.The two interior opposite angles of a triangle are 24° and 36°. What is the exterior angle (in degrees)?
  38. 38.An exterior angle of a triangle is 86°. One of its two interior opposite angles is 33°. What is the other one (in degrees)?
  39. 39.In a right-angled triangle, one of the other two angles is 33°. What is the third angle (in degrees)?
  40. 40.The angles of a triangle are in the ratio 1 : 1 : 2. What is the biggest angle (in degrees)?

Answer key

  1. 8
  2. 60
  3. No
  4. 133
  5. 48
  6. 78
  7. No
  8. 20
  9. Yes
  10. 58
  11. 80
  12. 40
  13. 49
  14. No
  15. No
  16. 48
  17. 83
  18. 132
  19. 69
  20. 25
  21. 20
  22. 100
  23. 3
  24. 31
  25. 54
  26. 71
  27. 106
  28. 67
  29. 18
  30. 49
  31. No
  32. 12
  33. 60
  34. 21
  35. 15
  36. 52
  37. 60
  38. 53
  39. 57
  40. 90

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