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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 787 · 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.

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  1. 1.In a right-angled triangle, one of the other two angles is 40°. What is the third angle (in degrees)?
  2. 2.The angles of a triangle are in the ratio 2 : 3 : 4. What is the smallest angle (in degrees)?
  3. 3.An exterior angle of a triangle is 88°. One of its two interior opposite angles is 41°. What is the other one (in degrees)?
  4. 4.In an isosceles triangle, the angle between the two equal sides is 86°. What is each of the other two angles (in degrees)?
  5. 5.The angles of a triangle are in the ratio 1 : 2 : 2. What is the smallest angle (in degrees)?
  6. 6.In triangle ABC, angle A = 26° and angle B = 119°. What is angle C (in degrees)?
  7. 7.In an isosceles triangle, the two equal angles are 23° each. What is the third angle (in degrees)?
  8. 8.In triangle ABC, angle A = 23° and angle B = 104°. What is angle C (in degrees)?
  9. 9.An exterior angle of a triangle is 104°. One of its two interior opposite angles is 42°. What is the other one (in degrees)?
  10. 10.An exterior angle of a triangle is 75°. One of its two interior opposite angles is 36°. What is the other one (in degrees)?
  11. 11.The angles of a triangle are in the ratio 1 : 4 : 5. What is the smallest angle (in degrees)?
  12. 12.In triangle ABC, angle A = 48° and angle B = 90°. What is angle C (in degrees)?
  13. 13.In an isosceles triangle, the angle between the two equal sides is 144°. What is each of the other two angles (in degrees)?
  14. 14.Can a triangle have sides of 2 cm, 7 cm and 11 cm? (a) Yes (b) No
  15. 15.In triangle ABC, angle A = 42° and angle B = 55°. What is angle C (in degrees)?
  16. 16.In triangle ABC, angle A = 70° and angle B = 52°. What is angle C (in degrees)?
  17. 17.An exterior angle of a triangle is 78°. One of its two interior opposite angles is 56°. What is the other one (in degrees)?
  18. 18.The longest side of a right-angled triangle is 13 cm and one of the other sides is 12 cm. How long is the third side (in cm)?
  19. 19.Can a triangle have sides of 19 cm, 8 cm and 8 cm? (a) Yes (b) No
  20. 20.Can a triangle have sides of 5 cm, 17 cm and 8 cm? (a) No (b) Yes
  21. 21.In an isosceles triangle, the angle between the two equal sides is 52°. What is each of the other two angles (in degrees)?
  22. 22.In a right-angled triangle, one of the other two angles is 16°. What is the third angle (in degrees)?
  23. 23.The two shorter sides of a right-angled triangle are 8 cm and 15 cm. How long is the longest side (in cm)?
  24. 24.In an isosceles triangle, the two equal angles are 46° each. What is the third angle (in degrees)?
  25. 25.In an isosceles triangle, the angle between the two equal sides is 118°. What is each of the other two angles (in degrees)?
  26. 26.An exterior angle of a triangle is 76°. One of its two interior opposite angles is 47°. What is the other one (in degrees)?
  27. 27.The angles of a triangle are in the ratio 2 : 2 : 5. What is the biggest angle (in degrees)?
  28. 28.In an isosceles triangle, the angle between the two equal sides is 70°. What is each of the other two angles (in degrees)?
  29. 29.In a right-angled triangle, one of the other two angles is 64°. What is the third angle (in degrees)?
  30. 30.In a right-angled triangle, one of the other two angles is 28°. What is the third angle (in degrees)?
  31. 31.The two interior opposite angles of a triangle are 32° and 49°. What is the exterior angle (in degrees)?
  32. 32.In triangle ABC, angle A = 45° and angle B = 33°. What is angle C (in degrees)?
  33. 33.An exterior angle of a triangle is 134°. One of its two interior opposite angles is 80°. What is the other one (in degrees)?
  34. 34.The angles of a triangle are in the ratio 3 : 5 : 7. What is the biggest angle (in degrees)?
  35. 35.In a right-angled triangle, one of the other two angles is 29°. What is the third angle (in degrees)?
  36. 36.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)?
  37. 37.An exterior angle of a triangle is 126°. One of its two interior opposite angles is 77°. What is the other one (in degrees)?
  38. 38.The two shorter sides of a right-angled triangle are 7 cm and 24 cm. How long is the longest side (in cm)?
  39. 39.In an isosceles triangle, the two equal angles are 58° each. What is the third angle (in degrees)?
  40. 40.The two interior opposite angles of a triangle are 31° and 47°. What is the exterior angle (in degrees)?

Answer key

  1. 50
  2. 40
  3. 47
  4. 47
  5. 36
  6. 35
  7. 134
  8. 53
  9. 62
  10. 39
  11. 18
  12. 42
  13. 18
  14. No
  15. 83
  16. 58
  17. 22
  18. 5
  19. No
  20. No
  21. 64
  22. 74
  23. 17
  24. 88
  25. 31
  26. 29
  27. 100
  28. 55
  29. 26
  30. 62
  31. 81
  32. 102
  33. 54
  34. 84
  35. 61
  36. 24
  37. 49
  38. 25
  39. 64
  40. 78

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