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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 781 · 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 23° each. What is the third angle (in degrees)?
  2. 2.The two interior opposite angles of a triangle are 36° and 71°. What is the exterior angle (in degrees)?
  3. 3.In triangle ABC, angle A = 53° and angle B = 32°. What is angle C (in degrees)?
  4. 4.The angles of a triangle are in the ratio 1 : 2 : 6. What is the biggest angle (in degrees)?
  5. 5.Can a triangle have sides of 9 cm, 23 cm and 9 cm? (a) No (b) Yes
  6. 6.Can a triangle have sides of 5 cm, 13 cm and 5 cm? (a) No (b) Yes
  7. 7.In triangle ABC, angle A = 91° and angle B = 23°. What is angle C (in degrees)?
  8. 8.In a right-angled triangle, one of the other two angles is 14°. What is the third angle (in degrees)?
  9. 9.In triangle ABC, angle A = 26° and angle B = 124°. What is angle C (in degrees)?
  10. 10.The two interior opposite angles of a triangle are 54° and 65°. What is the exterior angle (in degrees)?
  11. 11.The two shorter sides of a right-angled triangle are 8 cm and 15 cm. How long is the longest side (in cm)?
  12. 12.Can a triangle have sides of 5 cm, 18 cm and 11 cm? (a) No (b) Yes
  13. 13.In a right-angled triangle, one of the other two angles is 25°. What is the third angle (in degrees)?
  14. 14.In a right-angled triangle, one of the other two angles is 20°. What is the third angle (in degrees)?
  15. 15.An exterior angle of a triangle is 126°. One of its two interior opposite angles is 58°. What is the other one (in degrees)?
  16. 16.In a right-angled triangle, one of the other two angles is 47°. What is the third angle (in degrees)?
  17. 17.In triangle ABC, angle A = 98° and angle B = 28°. What is angle C (in degrees)?
  18. 18.In a right-angled triangle, one of the other two angles is 31°. What is the third angle (in degrees)?
  19. 19.Can a triangle have sides of 12 cm, 12 cm and 6 cm? (a) No (b) Yes
  20. 20.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)?
  21. 21.The angles of a triangle are in the ratio 2 : 2 : 5. What is the smallest angle (in degrees)?
  22. 22.The two shorter sides of a right-angled triangle are 36 cm and 15 cm. How long is the longest side (in cm)?
  23. 23.In triangle ABC, angle A = 40° and angle B = 55°. What is angle C (in degrees)?
  24. 24.The two shorter sides of a right-angled triangle are 12 cm and 5 cm. How long is the longest side (in cm)?
  25. 25.In a right-angled triangle, one of the other two angles is 72°. What is the third angle (in degrees)?
  26. 26.An exterior angle of a triangle is 96°. One of its two interior opposite angles is 58°. What is the other one (in degrees)?
  27. 27.In an isosceles triangle, the angle between the two equal sides is 142°. What is each of the other two angles (in degrees)?
  28. 28.In a right-angled triangle, one of the other two angles is 54°. What is the third angle (in degrees)?
  29. 29.In an isosceles triangle, the angle between the two equal sides is 116°. What is each of the other two angles (in degrees)?
  30. 30.The angles of a triangle are in the ratio 1 : 3 : 5. What is the smallest angle (in degrees)?
  31. 31.In triangle ABC, angle A = 78° and angle B = 55°. What is angle C (in degrees)?
  32. 32.The two interior opposite angles of a triangle are 32° and 55°. What is the exterior angle (in degrees)?
  33. 33.In triangle ABC, angle A = 96° and angle B = 40°. What is angle C (in degrees)?
  34. 34.In triangle ABC, angle A = 32° and angle B = 26°. What is angle C (in degrees)?
  35. 35.The angles of a triangle are in the ratio 4 : 5 : 6. What is the smallest angle (in degrees)?
  36. 36.An exterior angle of a triangle is 79°. One of its two interior opposite angles is 57°. What is the other one (in degrees)?
  37. 37.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)?
  38. 38.In triangle ABC, angle A = 49° and angle B = 23°. What is angle C (in degrees)?
  39. 39.In an isosceles triangle, the two equal angles are 34° each. What is the third angle (in degrees)?
  40. 40.In a right-angled triangle, one of the other two angles is 27°. What is the third angle (in degrees)?

Answer key

  1. 134
  2. 107
  3. 95
  4. 120
  5. No
  6. No
  7. 66
  8. 76
  9. 30
  10. 119
  11. 17
  12. No
  13. 65
  14. 70
  15. 68
  16. 43
  17. 54
  18. 59
  19. Yes
  20. 6
  21. 40
  22. 39
  23. 85
  24. 13
  25. 18
  26. 38
  27. 19
  28. 36
  29. 32
  30. 20
  31. 47
  32. 87
  33. 44
  34. 122
  35. 48
  36. 22
  37. 8
  38. 108
  39. 112
  40. 63

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