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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 773 · 40 sums
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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 80° each. What is the third angle (in degrees)?
  2. 2.The two interior opposite angles of a triangle are 71° and 29°. What is the exterior angle (in degrees)?
  3. 3.In triangle ABC, angle A = 81° and angle B = 42°. What is angle C (in degrees)?
  4. 4.Can a triangle have sides of 11 cm, 20 cm and 9 cm? (a) No (b) Yes
  5. 5.In triangle ABC, angle A = 71° and angle B = 54°. What is angle C (in degrees)?
  6. 6.In an isosceles triangle, the two equal angles are 75° each. What is the third angle (in degrees)?
  7. 7.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)?
  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 an isosceles triangle, the two equal angles are 25° each. What is the third angle (in degrees)?
  10. 10.In triangle ABC, angle A = 36° and angle B = 37°. What is angle C (in degrees)?
  11. 11.The angles of a triangle are in the ratio 2 : 2 : 5. What is the biggest angle (in degrees)?
  12. 12.The angles of a triangle are in the ratio 2 : 3 : 5. What is the biggest angle (in degrees)?
  13. 13.Can a triangle have sides of 3 cm, 2 cm and 2 cm? (a) No (b) Yes
  14. 14.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)?
  15. 15.In an isosceles triangle, the angle between the two equal sides is 146°. What is each of the other two angles (in degrees)?
  16. 16.Can a triangle have sides of 8 cm, 12 cm and 12 cm? (a) No (b) Yes
  17. 17.The two shorter sides of a right-angled triangle are 8 cm and 15 cm. How long is the longest side (in cm)?
  18. 18.The two shorter sides of a right-angled triangle are 20 cm and 15 cm. How long is the longest side (in cm)?
  19. 19.An exterior angle of a triangle is 121°. One of its two interior opposite angles is 49°. What is the other one (in degrees)?
  20. 20.The two shorter sides of a right-angled triangle are 24 cm and 7 cm. How long is the longest side (in cm)?
  21. 21.An exterior angle of a triangle is 96°. One of its two interior opposite angles is 68°. What is the other one (in degrees)?
  22. 22.The angles of a triangle are in the ratio 5 : 6 : 7. What is the biggest angle (in degrees)?
  23. 23.An exterior angle of a triangle is 65°. One of its two interior opposite angles is 32°. What is the other one (in degrees)?
  24. 24.The longest side of a right-angled triangle is 25 cm and one of the other sides is 15 cm. How long is the third side (in cm)?
  25. 25.The two interior opposite angles of a triangle are 55° and 21°. What is the exterior angle (in degrees)?
  26. 26.Can a triangle have sides of 10 cm, 22 cm and 9 cm? (a) Yes (b) No
  27. 27.In triangle ABC, angle A = 69° and angle B = 67°. What is angle C (in degrees)?
  28. 28.In a right-angled triangle, one of the other two angles is 30°. What is the third angle (in degrees)?
  29. 29.In triangle ABC, angle A = 52° and angle B = 86°. What is angle C (in degrees)?
  30. 30.In an isosceles triangle, the angle between the two equal sides is 36°. What is each of the other two angles (in degrees)?
  31. 31.In an isosceles triangle, the angle between the two equal sides is 84°. What is each of the other two angles (in degrees)?
  32. 32.In a right-angled triangle, one of the other two angles is 11°. What is the third angle (in degrees)?
  33. 33.Can a triangle have sides of 5 cm, 3 cm and 7 cm? (a) No (b) Yes
  34. 34.An exterior angle of a triangle is 104°. One of its two interior opposite angles is 24°. What is the other one (in degrees)?
  35. 35.An exterior angle of a triangle is 134°. One of its two interior opposite angles is 70°. What is the other one (in degrees)?
  36. 36.Can a triangle have sides of 5 cm, 20 cm and 10 cm? (a) No (b) Yes
  37. 37.The angles of a triangle are in the ratio 2 : 7 : 9. What is the biggest angle (in degrees)?
  38. 38.An exterior angle of a triangle is 68°. One of its two interior opposite angles is 27°. What is the other one (in degrees)?
  39. 39.Can a triangle have sides of 24 cm, 10 cm and 10 cm? (a) Yes (b) No
  40. 40.In triangle ABC, angle A = 72° and angle B = 20°. What is angle C (in degrees)?

Answer key

  1. 20
  2. 100
  3. 57
  4. No
  5. 55
  6. 30
  7. 8
  8. 76
  9. 130
  10. 107
  11. 100
  12. 90
  13. Yes
  14. 16
  15. 17
  16. Yes
  17. 17
  18. 25
  19. 72
  20. 25
  21. 28
  22. 70
  23. 33
  24. 20
  25. 76
  26. No
  27. 44
  28. 60
  29. 42
  30. 72
  31. 48
  32. 79
  33. Yes
  34. 80
  35. 64
  36. No
  37. 90
  38. 41
  39. No
  40. 88

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