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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 671 · 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 an isosceles triangle, the angle between the two equal sides is 22°. What is each of the other two angles (in degrees)?
  2. 2.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)?
  3. 3.In a right-angled triangle, one of the other two angles is 50°. What is the third angle (in degrees)?
  4. 4.In triangle ABC, angle A = 100° and angle B = 39°. What is angle C (in degrees)?
  5. 5.In triangle ABC, angle A = 43° and angle B = 93°. What is angle C (in degrees)?
  6. 6.In an isosceles triangle, the angle between the two equal sides is 126°. What is each of the other two angles (in degrees)?
  7. 7.The angles of a triangle are in the ratio 1 : 4 : 5. What is the biggest angle (in degrees)?
  8. 8.In triangle ABC, angle A = 38° and angle B = 23°. What is angle C (in degrees)?
  9. 9.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)?
  10. 10.In a right-angled triangle, one of the other two angles is 45°. What is the third angle (in degrees)?
  11. 11.In a right-angled triangle, one of the other two angles is 26°. What is the third 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.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)?
  14. 14.In a right-angled triangle, one of the other two angles is 13°. What is the third angle (in degrees)?
  15. 15.In triangle ABC, angle A = 64° and angle B = 68°. What is angle C (in degrees)?
  16. 16.In an isosceles triangle, the angle between the two equal sides is 26°. What is each of the other two angles (in degrees)?
  17. 17.In an isosceles triangle, the two equal angles are 23° each. What is the third angle (in degrees)?
  18. 18.The longest side of a right-angled triangle is 26 cm and one of the other sides is 24 cm. How long is the third side (in cm)?
  19. 19.The angles of a triangle are in the ratio 2 : 2 : 5. What is the smallest angle (in degrees)?
  20. 20.In a right-angled triangle, one of the other two angles is 17°. What is the third angle (in degrees)?
  21. 21.The longest side of a right-angled triangle is 5 cm and one of the other sides is 3 cm. How long is the third side (in cm)?
  22. 22.The angles of a triangle are in the ratio 2 : 7 : 9. What is the biggest angle (in degrees)?
  23. 23.Can a triangle have sides of 10 cm, 23 cm and 10 cm? (a) Yes (b) No
  24. 24.The angles of a triangle are in the ratio 3 : 4 : 5. What is the smallest angle (in degrees)?
  25. 25.The two shorter sides of a right-angled triangle are 15 cm and 20 cm. How long is the longest side (in cm)?
  26. 26.In an isosceles triangle, the angle between the two equal sides is 46°. What is each of the other two angles (in degrees)?
  27. 27.In a right-angled triangle, one of the other two angles is 79°. What is the third angle (in degrees)?
  28. 28.Can a triangle have sides of 3 cm, 13 cm and 6 cm? (a) Yes (b) No
  29. 29.Can a triangle have sides of 10 cm, 12 cm and 3 cm? (a) Yes (b) No
  30. 30.In a right-angled triangle, one of the other two angles is 16°. What is the third angle (in degrees)?
  31. 31.Can a triangle have sides of 10 cm, 10 cm and 24 cm? (a) No (b) Yes
  32. 32.In triangle ABC, angle A = 33° and angle B = 79°. What is angle C (in degrees)?
  33. 33.In a right-angled triangle, one of the other two angles is 75°. What is the third angle (in degrees)?
  34. 34.In an isosceles triangle, the angle between the two equal sides is 128°. What is each of the other two angles (in degrees)?
  35. 35.In a right-angled triangle, one of the other two angles is 80°. What is the third angle (in degrees)?
  36. 36.The two interior opposite angles of a triangle are 49° and 46°. What is the exterior angle (in degrees)?
  37. 37.In a right-angled triangle, one of the other two angles is 21°. What is the third angle (in degrees)?
  38. 38.In an isosceles triangle, the two equal angles are 58° each. What is the third angle (in degrees)?
  39. 39.In a right-angled triangle, one of the other two angles is 48°. What is the third angle (in degrees)?
  40. 40.In a right-angled triangle, one of the other two angles is 11°. What is the third angle (in degrees)?

Answer key

  1. 79
  2. 7
  3. 40
  4. 41
  5. 44
  6. 27
  7. 90
  8. 119
  9. 8
  10. 45
  11. 64
  12. 90
  13. 15
  14. 77
  15. 48
  16. 77
  17. 134
  18. 10
  19. 40
  20. 73
  21. 4
  22. 90
  23. No
  24. 45
  25. 25
  26. 67
  27. 11
  28. No
  29. Yes
  30. 74
  31. No
  32. 68
  33. 15
  34. 26
  35. 10
  36. 95
  37. 69
  38. 64
  39. 42
  40. 79

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