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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 752 · 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.

NameDateTime takenScore ___ / 40
  1. 1.Can a triangle have sides of 5 cm, 3 cm and 3 cm? (a) Yes (b) No
  2. 2.In a right-angled triangle, one of the other two angles is 61°. What is the third angle (in degrees)?
  3. 3.Can a triangle have sides of 12 cm, 3 cm and 10 cm? (a) Yes (b) No
  4. 4.In an isosceles triangle, the angle between the two equal sides is 142°. What is each of the other two angles (in degrees)?
  5. 5.In an isosceles triangle, the angle between the two equal sides is 104°. What is each of the other two angles (in degrees)?
  6. 6.The angles of a triangle are in the ratio 1 : 1 : 2. What is the biggest angle (in degrees)?
  7. 7.In triangle ABC, angle A = 49° and angle B = 105°. What is angle C (in degrees)?
  8. 8.In an isosceles triangle, the two equal angles are 24° each. What is the third angle (in degrees)?
  9. 9.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)?
  10. 10.In a right-angled triangle, one of the other two angles is 69°. What is the third angle (in degrees)?
  11. 11.In triangle ABC, angle A = 72° and angle B = 67°. What is angle C (in degrees)?
  12. 12.The angles of a triangle are in the ratio 1 : 1 : 2. What is the smallest angle (in degrees)?
  13. 13.Can a triangle have sides of 11 cm, 10 cm and 24 cm? (a) No (b) Yes
  14. 14.In a right-angled triangle, one of the other two angles is 36°. What is the third angle (in degrees)?
  15. 15.Can a triangle have sides of 10 cm, 20 cm and 10 cm? (a) Yes (b) No
  16. 16.The angles of a triangle are in the ratio 1 : 4 : 5. What is the biggest angle (in degrees)?
  17. 17.In a right-angled triangle, one of the other two angles is 40°. What is the third angle (in degrees)?
  18. 18.In an isosceles triangle, the two equal angles are 56° each. What is the third angle (in degrees)?
  19. 19.In triangle ABC, angle A = 94° and angle B = 31°. What is angle C (in degrees)?
  20. 20.In a right-angled triangle, one of the other two angles is 15°. What is the third angle (in degrees)?
  21. 21.In triangle ABC, angle A = 75° and angle B = 20°. What is angle C (in degrees)?
  22. 22.In an isosceles triangle, the two equal angles are 60° each. What is the third angle (in degrees)?
  23. 23.The two interior opposite angles of a triangle are 21° and 74°. What is the exterior angle (in degrees)?
  24. 24.In triangle ABC, angle A = 24° and angle B = 57°. What is angle C (in degrees)?
  25. 25.The two shorter sides of a right-angled triangle are 10 cm and 24 cm. How long is the longest side (in cm)?
  26. 26.An exterior angle of a triangle is 89°. One of its two interior opposite angles is 61°. What is the other one (in degrees)?
  27. 27.The longest side of a right-angled triangle is 26 cm and one of the other sides is 10 cm. How long is the third side (in cm)?
  28. 28.An exterior angle of a triangle is 150°. One of its two interior opposite angles is 80°. What is the other one (in degrees)?
  29. 29.In triangle ABC, angle A = 87° and angle B = 38°. What is angle C (in degrees)?
  30. 30.Can a triangle have sides of 2 cm, 10 cm and 4 cm? (a) Yes (b) No
  31. 31.Can a triangle have sides of 12 cm, 22 cm and 6 cm? (a) Yes (b) No
  32. 32.The two interior opposite angles of a triangle are 58° and 20°. What is the exterior angle (in degrees)?
  33. 33.In a right-angled triangle, one of the other two angles is 27°. What is the third angle (in degrees)?
  34. 34.The two shorter sides of a right-angled triangle are 8 cm and 15 cm. How long is the longest side (in cm)?
  35. 35.In an isosceles triangle, the angle between the two equal sides is 100°. What is each of the other two angles (in degrees)?
  36. 36.The angles of a triangle are in the ratio 2 : 2 : 5. What is the biggest angle (in degrees)?
  37. 37.The two shorter sides of a right-angled triangle are 8 cm and 6 cm. How long is the longest side (in cm)?
  38. 38.Can a triangle have sides of 5 cm, 9 cm and 17 cm? (a) Yes (b) No
  39. 39.The angles of a triangle are in the ratio 4 : 5 : 6. What is the biggest angle (in degrees)?
  40. 40.In triangle ABC, angle A = 30° and angle B = 120°. What is angle C (in degrees)?

Answer key

  1. Yes
  2. 29
  3. Yes
  4. 19
  5. 38
  6. 90
  7. 26
  8. 132
  9. 15
  10. 21
  11. 41
  12. 45
  13. No
  14. 54
  15. No
  16. 90
  17. 50
  18. 68
  19. 55
  20. 75
  21. 85
  22. 60
  23. 95
  24. 99
  25. 26
  26. 28
  27. 24
  28. 70
  29. 55
  30. No
  31. No
  32. 78
  33. 63
  34. 17
  35. 40
  36. 100
  37. 10
  38. No
  39. 72
  40. 30

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