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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 735 · 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.An exterior angle of a triangle is 53°. One of its two interior opposite angles is 31°. What is the other one (in degrees)?
  2. 2.In an isosceles triangle, the angle between the two equal sides is 20°. What is each of the other two angles (in degrees)?
  3. 3.The angles of a triangle are in the ratio 1 : 1 : 2. What is the smallest angle (in degrees)?
  4. 4.The two shorter sides of a right-angled triangle are 7 cm and 24 cm. How long is the longest side (in cm)?
  5. 5.Can a triangle have sides of 3 cm, 18 cm and 12 cm? (a) No (b) Yes
  6. 6.The two interior opposite angles of a triangle are 30° and 31°. What is the exterior angle (in degrees)?
  7. 7.In triangle ABC, angle A = 79° and angle B = 45°. What is angle C (in degrees)?
  8. 8.The longest side of a right-angled triangle is 20 cm and one of the other sides is 16 cm. How long is the third side (in cm)?
  9. 9.An exterior angle of a triangle is 113°. One of its two interior opposite angles is 41°. What is the other one (in degrees)?
  10. 10.In a right-angled triangle, one of the other two angles is 16°. What is the third angle (in degrees)?
  11. 11.In triangle ABC, angle A = 86° and angle B = 33°. What is angle C (in degrees)?
  12. 12.In triangle ABC, angle A = 63° and angle B = 46°. What is angle C (in degrees)?
  13. 13.Can a triangle have sides of 17 cm, 7 cm and 7 cm? (a) Yes (b) No
  14. 14.Can a triangle have sides of 3 cm, 12 cm and 4 cm? (a) No (b) Yes
  15. 15.In triangle ABC, angle A = 41° and angle B = 81°. What is angle C (in degrees)?
  16. 16.The angles of a triangle are in the ratio 2 : 3 : 5. What is the smallest angle (in degrees)?
  17. 17.An exterior angle of a triangle is 107°. One of its two interior opposite angles is 43°. What is the other one (in degrees)?
  18. 18.In triangle ABC, angle A = 71° and angle B = 67°. What is angle C (in degrees)?
  19. 19.In a right-angled triangle, one of the other two angles is 25°. What is the third angle (in degrees)?
  20. 20.The angles of a triangle are in the ratio 4 : 5 : 6. What is the smallest angle (in degrees)?
  21. 21.The two interior opposite angles of a triangle are 25° and 26°. What is the exterior angle (in degrees)?
  22. 22.In triangle ABC, angle A = 40° and angle B = 104°. What is angle C (in degrees)?
  23. 23.Can a triangle have sides of 6 cm, 9 cm and 7 cm? (a) Yes (b) No
  24. 24.The angles of a triangle are in the ratio 1 : 2 : 6. What is the biggest angle (in degrees)?
  25. 25.An exterior angle of a triangle is 88°. One of its two interior opposite angles is 30°. What is the other one (in degrees)?
  26. 26.In an isosceles triangle, the angle between the two equal sides is 66°. What is each of the other two angles (in degrees)?
  27. 27.In an isosceles triangle, the angle between the two equal sides is 92°. What is each of the other two angles (in degrees)?
  28. 28.Can a triangle have sides of 10 cm, 22 cm and 12 cm? (a) Yes (b) No
  29. 29.The two interior opposite angles of a triangle are 27° and 73°. What is the exterior angle (in degrees)?
  30. 30.The two interior opposite angles of a triangle are 29° and 28°. What is the exterior angle (in degrees)?
  31. 31.In a right-angled triangle, one of the other two angles is 12°. What is the third angle (in degrees)?
  32. 32.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)?
  33. 33.The longest side of a right-angled triangle is 15 cm and one of the other sides is 12 cm. How long is the third side (in cm)?
  34. 34.Can a triangle have sides of 6 cm, 11 cm and 6 cm? (a) Yes (b) No
  35. 35.An exterior angle of a triangle is 73°. One of its two interior opposite angles is 50°. What is the other one (in degrees)?
  36. 36.In triangle ABC, angle A = 58° and angle B = 30°. What is angle C (in degrees)?
  37. 37.In a right-angled triangle, one of the other two angles is 28°. What is the third angle (in degrees)?
  38. 38.In a right-angled triangle, one of the other two angles is 61°. What is the third angle (in degrees)?
  39. 39.Can a triangle have sides of 16 cm, 8 cm and 8 cm? (a) No (b) Yes
  40. 40.An exterior angle of a triangle is 128°. One of its two interior opposite angles is 76°. What is the other one (in degrees)?

Answer key

  1. 22
  2. 80
  3. 45
  4. 25
  5. No
  6. 61
  7. 56
  8. 12
  9. 72
  10. 74
  11. 61
  12. 71
  13. No
  14. No
  15. 58
  16. 36
  17. 64
  18. 42
  19. 65
  20. 48
  21. 51
  22. 36
  23. Yes
  24. 120
  25. 58
  26. 57
  27. 44
  28. No
  29. 100
  30. 57
  31. 78
  32. 8
  33. 9
  34. Yes
  35. 23
  36. 92
  37. 62
  38. 29
  39. No
  40. 52

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