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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 627 · 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.The angles of a triangle are in the ratio 1 : 2 : 6. What is the biggest angle (in degrees)?
  2. 2.In a right-angled triangle, one of the other two angles is 41°. What is the third angle (in degrees)?
  3. 3.Can a triangle have sides of 4 cm, 1 cm and 4 cm? (a) No (b) Yes
  4. 4.The angles of a triangle are in the ratio 3 : 5 : 7. What is the biggest angle (in degrees)?
  5. 5.In triangle ABC, angle A = 43° and angle B = 72°. What is angle C (in degrees)?
  6. 6.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)?
  7. 7.In a right-angled triangle, one of the other two angles is 47°. What is the third angle (in degrees)?
  8. 8.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)?
  9. 9.The two interior opposite angles of a triangle are 43° and 60°. What is the exterior angle (in degrees)?
  10. 10.In triangle ABC, angle A = 55° and angle B = 46°. What is angle C (in degrees)?
  11. 11.The two interior opposite angles of a triangle are 23° and 26°. What is the exterior angle (in degrees)?
  12. 12.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)?
  13. 13.The longest side of a right-angled triangle is 10 cm and one of the other sides is 6 cm. How long is the third side (in cm)?
  14. 14.An exterior angle of a triangle is 117°. One of its two interior opposite angles is 74°. What is the other one (in degrees)?
  15. 15.The two interior opposite angles of a triangle are 26° and 45°. What is the exterior angle (in degrees)?
  16. 16.In triangle ABC, angle A = 72° and angle B = 40°. What is angle C (in degrees)?
  17. 17.In an isosceles triangle, the angle between the two equal sides is 136°. What is each of the other two angles (in degrees)?
  18. 18.Can a triangle have sides of 7 cm, 7 cm and 6 cm? (a) Yes (b) No
  19. 19.In an isosceles triangle, the angle between the two equal sides is 36°. What is each of the other two angles (in degrees)?
  20. 20.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)?
  21. 21.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)?
  22. 22.In triangle ABC, angle A = 78° and angle B = 73°. What is angle C (in degrees)?
  23. 23.The angles of a triangle are in the ratio 1 : 2 : 3. What is the smallest angle (in degrees)?
  24. 24.In an isosceles triangle, the angle between the two equal sides is 20°. What is each of the other two angles (in degrees)?
  25. 25.The angles of a triangle are in the ratio 3 : 3 : 4. What is the biggest angle (in degrees)?
  26. 26.The two interior opposite angles of a triangle are 33° and 70°. What is the exterior angle (in degrees)?
  27. 27.In an isosceles triangle, the angle between the two equal sides is 44°. What is each of the other two angles (in degrees)?
  28. 28.An exterior angle of a triangle is 153°. One of its two interior opposite angles is 76°. What is the other one (in degrees)?
  29. 29.In triangle ABC, angle A = 97° and angle B = 24°. What is angle C (in degrees)?
  30. 30.In an isosceles triangle, the two equal angles are 27° each. What is the third angle (in degrees)?
  31. 31.In triangle ABC, angle A = 74° and angle B = 52°. What is angle C (in degrees)?
  32. 32.In triangle ABC, angle A = 74° and angle B = 54°. What is angle C (in degrees)?
  33. 33.In an isosceles triangle, the two equal angles are 42° each. What is the third angle (in degrees)?
  34. 34.In triangle ABC, angle A = 25° and angle B = 33°. What is angle C (in degrees)?
  35. 35.In triangle ABC, angle A = 99° and angle B = 59°. What is angle C (in degrees)?
  36. 36.Can a triangle have sides of 11 cm, 7 cm and 2 cm? (a) Yes (b) No
  37. 37.In a right-angled triangle, one of the other two angles is 20°. What is the third angle (in degrees)?
  38. 38.The two interior opposite angles of a triangle are 32° and 33°. What is the exterior angle (in degrees)?
  39. 39.The two interior opposite angles of a triangle are 20° and 40°. What is the exterior angle (in degrees)?
  40. 40.In a right-angled triangle, one of the other two angles is 77°. What is the third angle (in degrees)?

Answer key

  1. 120
  2. 49
  3. Yes
  4. 84
  5. 65
  6. 7
  7. 43
  8. 12
  9. 103
  10. 79
  11. 49
  12. 15
  13. 8
  14. 43
  15. 71
  16. 68
  17. 22
  18. Yes
  19. 72
  20. 12
  21. 24
  22. 29
  23. 30
  24. 80
  25. 72
  26. 103
  27. 68
  28. 77
  29. 59
  30. 126
  31. 54
  32. 52
  33. 96
  34. 122
  35. 22
  36. No
  37. 70
  38. 65
  39. 60
  40. 13

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