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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 54 · 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 angles of a triangle are in the ratio 3 : 4 : 5. What is the smallest angle (in degrees)?
  2. 2.In triangle ABC, angle A = 39° and angle B = 55°. What is angle C (in degrees)?
  3. 3.In triangle ABC, angle A = 61° and angle B = 30°. What is angle C (in degrees)?
  4. 4.In a right-angled triangle, one of the other two angles is 17°. What is the third angle (in degrees)?
  5. 5.The longest side of a right-angled triangle is 26 cm and one of the other sides is 24 cm. How long is the third side (in cm)?
  6. 6.In an isosceles triangle, the angle between the two equal sides is 74°. What is each of the other two angles (in degrees)?
  7. 7.The angles of a triangle are in the ratio 2 : 2 : 5. What is the smallest angle (in degrees)?
  8. 8.In a right-angled triangle, one of the other two angles is 16°. What is the third angle (in degrees)?
  9. 9.In an isosceles triangle, the two equal angles are 46° each. What is the third angle (in degrees)?
  10. 10.Can a triangle have sides of 12 cm, 23 cm and 9 cm? (a) Yes (b) No
  11. 11.In triangle ABC, angle A = 44° and angle B = 111°. What is angle C (in degrees)?
  12. 12.In triangle ABC, angle A = 32° and angle B = 72°. What is angle C (in degrees)?
  13. 13.The two shorter sides of a right-angled triangle are 8 cm and 15 cm. How long is the longest side (in cm)?
  14. 14.In an isosceles triangle, the two equal angles are 38° each. What is the third angle (in degrees)?
  15. 15.In an isosceles triangle, the two equal angles are 43° each. What is the third angle (in degrees)?
  16. 16.In an isosceles triangle, the angle between the two equal sides is 96°. What is each of the other two angles (in degrees)?
  17. 17.In a right-angled triangle, one of the other two angles is 13°. What is the third angle (in degrees)?
  18. 18.In an isosceles triangle, the angle between the two equal sides is 50°. What is each of the other two angles (in degrees)?
  19. 19.An exterior angle of a triangle is 86°. One of its two interior opposite angles is 57°. What is the other one (in degrees)?
  20. 20.Can a triangle have sides of 8 cm, 8 cm and 3 cm? (a) Yes (b) No
  21. 21.An exterior angle of a triangle is 105°. One of its two interior opposite angles is 33°. What is the other one (in degrees)?
  22. 22.The angles of a triangle are in the ratio 1 : 1 : 2. What is the smallest angle (in degrees)?
  23. 23.In a right-angled triangle, one of the other two angles is 23°. What is the third angle (in degrees)?
  24. 24.In an isosceles triangle, the two equal angles are 24° each. What is the third angle (in degrees)?
  25. 25.Can a triangle have sides of 23 cm, 10 cm and 11 cm? (a) Yes (b) No
  26. 26.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)?
  27. 27.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)?
  28. 28.The angles of a triangle are in the ratio 5 : 6 : 7. What is the smallest angle (in degrees)?
  29. 29.In an isosceles triangle, the angle between the two equal sides is 108°. What is each of the other two angles (in degrees)?
  30. 30.In a right-angled triangle, one of the other two angles is 11°. What is the third angle (in degrees)?
  31. 31.An exterior angle of a triangle is 49°. One of its two interior opposite angles is 20°. What is the other one (in degrees)?
  32. 32.The angles of a triangle are in the ratio 3 : 4 : 5. What is the biggest angle (in degrees)?
  33. 33.The two interior opposite angles of a triangle are 27° and 77°. What is the exterior angle (in degrees)?
  34. 34.In triangle ABC, angle A = 83° and angle B = 36°. What is angle C (in degrees)?
  35. 35.The angles of a triangle are in the ratio 1 : 3 : 5. What is the smallest angle (in degrees)?
  36. 36.The two shorter sides of a right-angled triangle are 15 cm and 8 cm. How long is the longest side (in cm)?
  37. 37.In triangle ABC, angle A = 21° and angle B = 59°. What is angle C (in degrees)?
  38. 38.The longest side of a right-angled triangle is 13 cm and one of the other sides is 5 cm. How long is the third side (in cm)?
  39. 39.The two interior opposite angles of a triangle are 61° and 23°. What is the exterior angle (in degrees)?
  40. 40.The two interior opposite angles of a triangle are 64° and 63°. What is the exterior angle (in degrees)?

Answer key

  1. 45
  2. 86
  3. 89
  4. 73
  5. 10
  6. 53
  7. 40
  8. 74
  9. 88
  10. No
  11. 25
  12. 76
  13. 17
  14. 104
  15. 94
  16. 42
  17. 77
  18. 65
  19. 29
  20. Yes
  21. 72
  22. 45
  23. 67
  24. 132
  25. No
  26. 24
  27. 16
  28. 50
  29. 36
  30. 79
  31. 29
  32. 75
  33. 104
  34. 61
  35. 20
  36. 17
  37. 100
  38. 12
  39. 84
  40. 127

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