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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 849 · 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.Can a triangle have sides of 18 cm, 7 cm and 7 cm? (a) Yes (b) No
  2. 2.The angles of a triangle are in the ratio 2 : 7 : 9. What is the smallest angle (in degrees)?
  3. 3.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)?
  4. 4.In a right-angled triangle, one of the other two angles is 34°. What is the third angle (in degrees)?
  5. 5.The two interior opposite angles of a triangle are 65° and 59°. What is the exterior angle (in degrees)?
  6. 6.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)?
  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 two interior opposite angles of a triangle are 68° and 53°. What is the exterior angle (in degrees)?
  9. 9.The two interior opposite angles of a triangle are 27° and 59°. What is the exterior angle (in degrees)?
  10. 10.In triangle ABC, angle A = 95° and angle B = 60°. What is angle C (in degrees)?
  11. 11.In a right-angled triangle, one of the other two angles is 38°. What is the third angle (in degrees)?
  12. 12.In a right-angled triangle, one of the other two angles is 26°. What is the third angle (in degrees)?
  13. 13.In a right-angled triangle, one of the other two angles is 48°. What is the third angle (in degrees)?
  14. 14.In an isosceles triangle, the two equal angles are 72° each. What is the third angle (in degrees)?
  15. 15.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)?
  16. 16.In triangle ABC, angle A = 100° and angle B = 21°. What is angle C (in degrees)?
  17. 17.The angles of a triangle are in the ratio 2 : 3 : 4. What is the biggest angle (in degrees)?
  18. 18.In an isosceles triangle, the angle between the two equal sides is 74°. What is each of the other two angles (in degrees)?
  19. 19.In a right-angled triangle, one of the other two angles is 51°. What is the third angle (in degrees)?
  20. 20.The angles of a triangle are in the ratio 1 : 1 : 2. What is the smallest angle (in degrees)?
  21. 21.Can a triangle have sides of 4 cm, 4 cm and 6 cm? (a) No (b) Yes
  22. 22.The angles of a triangle are in the ratio 3 : 4 : 5. What is the smallest angle (in degrees)?
  23. 23.In an isosceles triangle, the angle between the two equal sides is 124°. What is each of the other two angles (in degrees)?
  24. 24.In an isosceles triangle, the angle between the two equal sides is 132°. What is each of the other two angles (in degrees)?
  25. 25.In an isosceles triangle, the angle between the two equal sides is 68°. What is each of the other two angles (in degrees)?
  26. 26.In an isosceles triangle, the two equal angles are 42° each. What is the third angle (in degrees)?
  27. 27.The two interior opposite angles of a triangle are 39° and 25°. What is the exterior angle (in degrees)?
  28. 28.In an isosceles triangle, the two equal angles are 57° each. What is the third angle (in degrees)?
  29. 29.An exterior angle of a triangle is 131°. One of its two interior opposite angles is 78°. What is the other one (in degrees)?
  30. 30.In an isosceles triangle, the two equal angles are 77° each. What is the third angle (in degrees)?
  31. 31.Can a triangle have sides of 10 cm, 4 cm and 15 cm? (a) Yes (b) No
  32. 32.The two interior opposite angles of a triangle are 60° and 44°. What is the exterior angle (in degrees)?
  33. 33.In triangle ABC, angle A = 60° and angle B = 92°. What is angle C (in degrees)?
  34. 34.The angles of a triangle are in the ratio 5 : 6 : 7. What is the smallest angle (in degrees)?
  35. 35.The angles of a triangle are in the ratio 1 : 2 : 3. What is the biggest angle (in degrees)?
  36. 36.In triangle ABC, angle A = 99° and angle B = 50°. What is angle C (in degrees)?
  37. 37.In an isosceles triangle, the angle between the two equal sides is 134°. What is each of the other two angles (in degrees)?
  38. 38.In triangle ABC, angle A = 49° and angle B = 40°. What is angle C (in degrees)?
  39. 39.In triangle ABC, angle A = 98° and angle B = 37°. What is angle C (in degrees)?
  40. 40.The two shorter sides of a right-angled triangle are 18 cm and 24 cm. How long is the longest side (in cm)?

Answer key

  1. No
  2. 20
  3. 8
  4. 56
  5. 124
  6. 24
  7. 43
  8. 121
  9. 86
  10. 25
  11. 52
  12. 64
  13. 42
  14. 36
  15. 7
  16. 59
  17. 80
  18. 53
  19. 39
  20. 45
  21. Yes
  22. 45
  23. 28
  24. 24
  25. 56
  26. 96
  27. 64
  28. 66
  29. 53
  30. 26
  31. No
  32. 104
  33. 28
  34. 50
  35. 90
  36. 31
  37. 23
  38. 91
  39. 45
  40. 30

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