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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 799 · 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.In an isosceles triangle, the two equal angles are 59° each. What is the third angle (in degrees)?
  2. 2.In a right-angled triangle, one of the other two angles is 23°. What is the third angle (in degrees)?
  3. 3.Can a triangle have sides of 11 cm, 8 cm and 8 cm? (a) Yes (b) No
  4. 4.The longest side of a right-angled triangle is 25 cm and one of the other sides is 24 cm. How long is the third side (in cm)?
  5. 5.The angles of a triangle are in the ratio 2 : 2 : 5. What is the smallest angle (in degrees)?
  6. 6.In triangle ABC, angle A = 91° and angle B = 21°. What is angle C (in degrees)?
  7. 7.In a right-angled triangle, one of the other two angles is 79°. What is the third angle (in degrees)?
  8. 8.Can a triangle have sides of 5 cm, 10 cm and 16 cm? (a) Yes (b) No
  9. 9.In a right-angled triangle, one of the other two angles is 29°. What is the third angle (in degrees)?
  10. 10.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)?
  11. 11.The two interior opposite angles of a triangle are 72° and 43°. What is the exterior angle (in degrees)?
  12. 12.An exterior angle of a triangle is 81°. One of its two interior opposite angles is 50°. What is the other one (in degrees)?
  13. 13.An exterior angle of a triangle is 107°. One of its two interior opposite angles is 48°. What is the other one (in degrees)?
  14. 14.In an isosceles triangle, the two equal angles are 64° each. What is the third angle (in degrees)?
  15. 15.The angles of a triangle are in the ratio 3 : 4 : 5. What is the smallest angle (in degrees)?
  16. 16.In triangle ABC, angle A = 77° and angle B = 34°. What is angle C (in degrees)?
  17. 17.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)?
  18. 18.In an isosceles triangle, the two equal angles are 67° each. What is the third angle (in degrees)?
  19. 19.Can a triangle have sides of 7 cm, 7 cm and 15 cm? (a) No (b) Yes
  20. 20.In triangle ABC, angle A = 31° and angle B = 93°. What is angle C (in degrees)?
  21. 21.In an isosceles triangle, the angle between the two equal sides is 32°. What is each of the other two angles (in degrees)?
  22. 22.In a right-angled triangle, one of the other two angles is 33°. What is the third angle (in degrees)?
  23. 23.The two interior opposite angles of a triangle are 64° and 60°. What is the exterior angle (in degrees)?
  24. 24.In triangle ABC, angle A = 24° and angle B = 75°. What is angle C (in degrees)?
  25. 25.The two interior opposite angles of a triangle are 62° and 50°. What is the exterior angle (in degrees)?
  26. 26.In a right-angled triangle, one of the other two angles is 21°. What is the third angle (in degrees)?
  27. 27.In triangle ABC, angle A = 91° and angle B = 39°. What is angle C (in degrees)?
  28. 28.The longest side of a right-angled triangle is 20 cm and one of the other sides is 12 cm. How long is the third side (in cm)?
  29. 29.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)?
  30. 30.The two interior opposite angles of a triangle are 72° and 36°. What is the exterior angle (in degrees)?
  31. 31.Can a triangle have sides of 2 cm, 15 cm and 9 cm? (a) No (b) Yes
  32. 32.The two interior opposite angles of a triangle are 43° and 59°. What is the exterior angle (in degrees)?
  33. 33.The two interior opposite angles of a triangle are 31° and 35°. What is the exterior angle (in degrees)?
  34. 34.The angles of a triangle are in the ratio 1 : 2 : 2. What is the biggest angle (in degrees)?
  35. 35.The longest side of a right-angled triangle is 39 cm and one of the other sides is 15 cm. How long is the third side (in cm)?
  36. 36.An exterior angle of a triangle is 152°. One of its two interior opposite angles is 73°. What is the other one (in degrees)?
  37. 37.In triangle ABC, angle A = 60° and angle B = 49°. What is angle C (in degrees)?
  38. 38.The two interior opposite angles of a triangle are 29° and 62°. What is the exterior angle (in degrees)?
  39. 39.The angles of a triangle are in the ratio 5 : 6 : 7. What is the smallest angle (in degrees)?
  40. 40.In a right-angled triangle, one of the other two angles is 55°. What is the third angle (in degrees)?

Answer key

  1. 62
  2. 67
  3. Yes
  4. 7
  5. 40
  6. 68
  7. 11
  8. No
  9. 61
  10. 15
  11. 115
  12. 31
  13. 59
  14. 52
  15. 45
  16. 69
  17. 8
  18. 46
  19. No
  20. 56
  21. 74
  22. 57
  23. 124
  24. 81
  25. 112
  26. 69
  27. 50
  28. 16
  29. 6
  30. 108
  31. No
  32. 102
  33. 66
  34. 72
  35. 36
  36. 79
  37. 71
  38. 91
  39. 50
  40. 35

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