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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 543 · 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 two interior opposite angles of a triangle are 34° and 20°. What is the exterior angle (in degrees)?
  2. 2.In triangle ABC, angle A = 39° and angle B = 99°. What is angle C (in degrees)?
  3. 3.Can a triangle have sides of 6 cm, 15 cm and 12 cm? (a) No (b) Yes
  4. 4.In triangle ABC, angle A = 100° and angle B = 34°. What is angle C (in degrees)?
  5. 5.The angles of a triangle are in the ratio 2 : 3 : 5. What is the smallest angle (in degrees)?
  6. 6.The two shorter sides of a right-angled triangle are 5 cm and 12 cm. How long is the longest side (in cm)?
  7. 7.The angles of a triangle are in the ratio 5 : 6 : 7. What is the biggest angle (in degrees)?
  8. 8.The angles of a triangle are in the ratio 4 : 5 : 6. What is the biggest angle (in degrees)?
  9. 9.An exterior angle of a triangle is 88°. One of its two interior opposite angles is 55°. What is the other one (in degrees)?
  10. 10.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)?
  11. 11.An exterior angle of a triangle is 95°. One of its two interior opposite angles is 63°. What is the other one (in degrees)?
  12. 12.In an isosceles triangle, the angle between the two equal sides is 108°. What is each of the other two angles (in degrees)?
  13. 13.In an isosceles triangle, the angle between the two equal sides is 104°. What is each of the other two angles (in degrees)?
  14. 14.The angles of a triangle are in the ratio 2 : 2 : 5. What is the biggest angle (in degrees)?
  15. 15.In a right-angled triangle, one of the other two angles is 14°. What is the third angle (in degrees)?
  16. 16.Can a triangle have sides of 11 cm, 10 cm and 9 cm? (a) No (b) Yes
  17. 17.Can a triangle have sides of 10 cm, 22 cm and 11 cm? (a) Yes (b) No
  18. 18.In triangle ABC, angle A = 26° and angle B = 76°. What is angle C (in degrees)?
  19. 19.In triangle ABC, angle A = 38° and angle B = 73°. What is angle C (in degrees)?
  20. 20.Can a triangle have sides of 7 cm, 7 cm and 17 cm? (a) Yes (b) No
  21. 21.The two interior opposite angles of a triangle are 80° and 50°. What is the exterior angle (in degrees)?
  22. 22.The two interior opposite angles of a triangle are 69° and 63°. What is the exterior angle (in degrees)?
  23. 23.In triangle ABC, angle A = 68° and angle B = 31°. What is angle C (in degrees)?
  24. 24.An exterior angle of a triangle is 143°. One of its two interior opposite angles is 75°. What is the other one (in degrees)?
  25. 25.An exterior angle of a triangle is 76°. One of its two interior opposite angles is 25°. What is the other one (in degrees)?
  26. 26.In an isosceles triangle, the two equal angles are 21° each. What is the third angle (in degrees)?
  27. 27.An exterior angle of a triangle is 103°. One of its two interior opposite angles is 35°. What is the other one (in degrees)?
  28. 28.In a right-angled triangle, one of the other two angles is 11°. What is the third angle (in degrees)?
  29. 29.In a right-angled triangle, one of the other two angles is 67°. What is the third angle (in degrees)?
  30. 30.In a right-angled triangle, one of the other two angles is 51°. What is the third angle (in degrees)?
  31. 31.In triangle ABC, angle A = 28° and angle B = 107°. What is angle C (in degrees)?
  32. 32.The longest side of a right-angled triangle is 15 cm and one of the other sides is 9 cm. How long is the third side (in cm)?
  33. 33.In triangle ABC, angle A = 86° and angle B = 34°. What is angle C (in degrees)?
  34. 34.The angles of a triangle are in the ratio 1 : 2 : 6. What is the smallest angle (in degrees)?
  35. 35.An exterior angle of a triangle is 55°. One of its two interior opposite angles is 35°. What is the other one (in degrees)?
  36. 36.In an isosceles triangle, the angle between the two equal sides is 28°. What is each of the other two angles (in degrees)?
  37. 37.In triangle ABC, angle A = 26° and angle B = 70°. What is angle C (in degrees)?
  38. 38.In triangle ABC, angle A = 94° and angle B = 33°. What is angle C (in degrees)?
  39. 39.In triangle ABC, angle A = 66° and angle B = 85°. What is angle C (in degrees)?
  40. 40.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)?

Answer key

  1. 54
  2. 42
  3. Yes
  4. 46
  5. 36
  6. 13
  7. 70
  8. 72
  9. 33
  10. 7
  11. 32
  12. 36
  13. 38
  14. 100
  15. 76
  16. Yes
  17. No
  18. 78
  19. 69
  20. No
  21. 130
  22. 132
  23. 81
  24. 68
  25. 51
  26. 138
  27. 68
  28. 79
  29. 23
  30. 39
  31. 45
  32. 12
  33. 60
  34. 20
  35. 20
  36. 76
  37. 84
  38. 53
  39. 29
  40. 16

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