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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 165 · 40 sums
TalentJR

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 two equal angles are 42° each. What is the third angle (in degrees)?
  2. 2.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)?
  3. 3.In an isosceles triangle, the angle between the two equal sides is 72°. What is each of the other two angles (in degrees)?
  4. 4.In an isosceles triangle, the angle between the two equal sides is 126°. What is each of the other two angles (in degrees)?
  5. 5.In a right-angled triangle, one of the other two angles is 54°. What is the third angle (in degrees)?
  6. 6.The two shorter sides of a right-angled triangle are 5 cm and 12 cm. How long is the longest side (in cm)?
  7. 7.The two interior opposite angles of a triangle are 68° and 70°. What is the exterior angle (in degrees)?
  8. 8.In a right-angled triangle, one of the other two angles is 38°. What is the third angle (in degrees)?
  9. 9.The two interior opposite angles of a triangle are 54° and 55°. What is the exterior angle (in degrees)?
  10. 10.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)?
  11. 11.The angles of a triangle are in the ratio 4 : 5 : 6. What is the biggest angle (in degrees)?
  12. 12.In a right-angled triangle, one of the other two angles is 17°. What is the third angle (in degrees)?
  13. 13.Can a triangle have sides of 12 cm, 9 cm and 7 cm? (a) Yes (b) No
  14. 14.In a right-angled triangle, one of the other two angles is 18°. What is the third angle (in degrees)?
  15. 15.The two interior opposite angles of a triangle are 59° and 21°. What is the exterior angle (in degrees)?
  16. 16.The angles of a triangle are in the ratio 2 : 3 : 5. What is the biggest angle (in degrees)?
  17. 17.The angles of a triangle are in the ratio 4 : 5 : 6. What is the smallest angle (in degrees)?
  18. 18.The angles of a triangle are in the ratio 2 : 2 : 5. What is the smallest angle (in degrees)?
  19. 19.In an isosceles triangle, the angle between the two equal sides is 110°. What is each of the other two angles (in degrees)?
  20. 20.In an isosceles triangle, the angle between the two equal sides is 70°. What is each of the other two angles (in degrees)?
  21. 21.In triangle ABC, angle A = 81° and angle B = 55°. What is angle C (in degrees)?
  22. 22.In triangle ABC, angle A = 87° and angle B = 46°. What is angle C (in degrees)?
  23. 23.Can a triangle have sides of 18 cm, 10 cm and 5 cm? (a) Yes (b) No
  24. 24.Can a triangle have sides of 9 cm, 19 cm and 9 cm? (a) Yes (b) No
  25. 25.In triangle ABC, angle A = 26° and angle B = 118°. What is angle C (in degrees)?
  26. 26.In triangle ABC, angle A = 97° and angle B = 35°. What is angle C (in degrees)?
  27. 27.In an isosceles triangle, the angle between the two equal sides is 140°. What is each of the other two angles (in degrees)?
  28. 28.In triangle ABC, angle A = 28° and angle B = 55°. What is angle C (in degrees)?
  29. 29.In an isosceles triangle, the angle between the two equal sides is 42°. What is each of the other two angles (in degrees)?
  30. 30.In a right-angled triangle, one of the other two angles is 27°. What is the third angle (in degrees)?
  31. 31.In a right-angled triangle, one of the other two angles is 26°. What is the third angle (in degrees)?
  32. 32.The longest side of a right-angled triangle is 5 cm and one of the other sides is 4 cm. How long is the third side (in cm)?
  33. 33.The angles of a triangle are in the ratio 3 : 5 : 7. What is the smallest angle (in degrees)?
  34. 34.In triangle ABC, angle A = 67° and angle B = 72°. What is angle C (in degrees)?
  35. 35.The angles of a triangle are in the ratio 1 : 2 : 2. What is the biggest angle (in degrees)?
  36. 36.In an isosceles triangle, the angle between the two equal sides is 84°. What is each of the other two angles (in degrees)?
  37. 37.In a right-angled triangle, one of the other two angles is 13°. What is the third angle (in degrees)?
  38. 38.In a right-angled triangle, one of the other two angles is 10°. What is the third angle (in degrees)?
  39. 39.The angles of a triangle are in the ratio 2 : 7 : 9. What is the smallest angle (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. 96
  2. 24
  3. 54
  4. 27
  5. 36
  6. 13
  7. 138
  8. 52
  9. 109
  10. 8
  11. 72
  12. 73
  13. Yes
  14. 72
  15. 80
  16. 90
  17. 48
  18. 40
  19. 35
  20. 55
  21. 44
  22. 47
  23. No
  24. No
  25. 36
  26. 48
  27. 20
  28. 97
  29. 69
  30. 63
  31. 64
  32. 3
  33. 36
  34. 41
  35. 72
  36. 48
  37. 77
  38. 80
  39. 20
  40. 30

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