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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 501 · 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.Can a triangle have sides of 9 cm, 6 cm and 10 cm? (a) Yes (b) No
  2. 2.An exterior angle of a triangle is 43°. One of its two interior opposite angles is 21°. What is the other one (in degrees)?
  3. 3.In a right-angled triangle, one of the other two angles is 76°. What is the third angle (in degrees)?
  4. 4.The angles of a triangle are in the ratio 3 : 4 : 5. What is the smallest angle (in degrees)?
  5. 5.Can a triangle have sides of 9 cm, 7 cm and 7 cm? (a) Yes (b) No
  6. 6.In triangle ABC, angle A = 87° and angle B = 53°. What is angle C (in degrees)?
  7. 7.In an isosceles triangle, the two equal angles are 20° each. What is the third angle (in degrees)?
  8. 8.The angles of a triangle are in the ratio 1 : 2 : 2. What is the smallest angle (in degrees)?
  9. 9.In triangle ABC, angle A = 73° and angle B = 67°. What is angle C (in degrees)?
  10. 10.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)?
  11. 11.The angles of a triangle are in the ratio 1 : 3 : 5. What is the smallest angle (in degrees)?
  12. 12.In an isosceles triangle, the two equal angles are 32° each. What is the third angle (in degrees)?
  13. 13.In an isosceles triangle, the two equal angles are 34° each. What is the third angle (in degrees)?
  14. 14.Can a triangle have sides of 5 cm, 6 cm and 15 cm? (a) No (b) Yes
  15. 15.In an isosceles triangle, the two equal angles are 83° each. What is the third angle (in degrees)?
  16. 16.In triangle ABC, angle A = 63° and angle B = 39°. What is angle C (in degrees)?
  17. 17.In triangle ABC, angle A = 68° and angle B = 66°. What is angle C (in degrees)?
  18. 18.In a right-angled triangle, one of the other two angles is 78°. What is the third angle (in degrees)?
  19. 19.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)?
  20. 20.In triangle ABC, angle A = 56° and angle B = 63°. What is angle C (in degrees)?
  21. 21.The angles of a triangle are in the ratio 1 : 4 : 5. What is the biggest angle (in degrees)?
  22. 22.In a right-angled triangle, one of the other two angles is 68°. What is the third angle (in degrees)?
  23. 23.Can a triangle have sides of 15 cm, 9 cm and 2 cm? (a) Yes (b) No
  24. 24.Can a triangle have sides of 15 cm, 11 cm and 9 cm? (a) No (b) Yes
  25. 25.In triangle ABC, angle A = 50° and angle B = 99°. What is angle C (in degrees)?
  26. 26.The angles of a triangle are in the ratio 3 : 5 : 7. What is the biggest angle (in degrees)?
  27. 27.In triangle ABC, angle A = 71° and angle B = 70°. What is angle C (in degrees)?
  28. 28.In triangle ABC, angle A = 26° and angle B = 97°. What is angle C (in degrees)?
  29. 29.The angles of a triangle are in the ratio 2 : 3 : 5. What is the smallest angle (in degrees)?
  30. 30.Can a triangle have sides of 6 cm, 5 cm and 9 cm? (a) Yes (b) No
  31. 31.Can a triangle have sides of 13 cm, 6 cm and 12 cm? (a) No (b) Yes
  32. 32.The angles of a triangle are in the ratio 1 : 2 : 3. What is the smallest angle (in degrees)?
  33. 33.The angles of a triangle are in the ratio 1 : 1 : 2. What is the biggest angle (in degrees)?
  34. 34.In an isosceles triangle, the two equal angles are 81° each. What is the third angle (in degrees)?
  35. 35.The angles of a triangle are in the ratio 2 : 7 : 9. What is the smallest angle (in degrees)?
  36. 36.In an isosceles triangle, the angle between the two equal sides is 142°. What is each of the other two angles (in degrees)?
  37. 37.In an isosceles triangle, the two equal angles are 24° each. What is the third angle (in degrees)?
  38. 38.The two interior opposite angles of a triangle are 29° and 61°. What is the exterior angle (in degrees)?
  39. 39.In triangle ABC, angle A = 60° and angle B = 74°. What is angle C (in degrees)?
  40. 40.In an isosceles triangle, the two equal angles are 57° each. What is the third angle (in degrees)?

Answer key

  1. Yes
  2. 22
  3. 14
  4. 45
  5. Yes
  6. 40
  7. 140
  8. 36
  9. 40
  10. 24
  11. 20
  12. 116
  13. 112
  14. No
  15. 14
  16. 78
  17. 46
  18. 12
  19. 9
  20. 61
  21. 90
  22. 22
  23. No
  24. Yes
  25. 31
  26. 84
  27. 39
  28. 57
  29. 36
  30. Yes
  31. Yes
  32. 30
  33. 90
  34. 18
  35. 20
  36. 19
  37. 132
  38. 90
  39. 46
  40. 66

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