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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 145 · 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 a right-angled triangle, one of the other two angles is 77°. What is the third angle (in degrees)?
  2. 2.The longest side of a right-angled triangle is 26 cm and one of the other sides is 10 cm. How long is the third side (in cm)?
  3. 3.In an isosceles triangle, the two equal angles are 31° each. What is the third angle (in degrees)?
  4. 4.In triangle ABC, angle A = 60° and angle B = 21°. What is angle C (in degrees)?
  5. 5.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)?
  6. 6.The two interior opposite angles of a triangle are 22° and 50°. What is the exterior angle (in degrees)?
  7. 7.The two shorter sides of a right-angled triangle are 8 cm and 15 cm. How long is the longest side (in cm)?
  8. 8.The two interior opposite angles of a triangle are 77° and 33°. What is the exterior angle (in degrees)?
  9. 9.In an isosceles triangle, the two equal angles are 36° each. What is the third angle (in degrees)?
  10. 10.In an isosceles triangle, the two equal angles are 81° each. What is the third angle (in degrees)?
  11. 11.In a right-angled triangle, one of the other two angles is 74°. What is the third angle (in degrees)?
  12. 12.In an isosceles triangle, the angle between the two equal sides is 72°. What is each of the other two angles (in degrees)?
  13. 13.An exterior angle of a triangle is 126°. One of its two interior opposite angles is 62°. What is the other one (in degrees)?
  14. 14.The two shorter sides of a right-angled triangle are 24 cm and 7 cm. How long is the longest side (in cm)?
  15. 15.The two interior opposite angles of a triangle are 28° and 38°. What is the exterior angle (in degrees)?
  16. 16.The angles of a triangle are in the ratio 1 : 2 : 6. What is the biggest angle (in degrees)?
  17. 17.Can a triangle have sides of 8 cm, 7 cm and 6 cm? (a) No (b) Yes
  18. 18.The angles of a triangle are in the ratio 1 : 1 : 2. What is the biggest angle (in degrees)?
  19. 19.The angles of a triangle are in the ratio 2 : 3 : 4. What is the biggest angle (in degrees)?
  20. 20.In triangle ABC, angle A = 82° and angle B = 32°. What is angle C (in degrees)?
  21. 21.An exterior angle of a triangle is 45°. One of its two interior opposite angles is 23°. What is the other one (in degrees)?
  22. 22.An exterior angle of a triangle is 123°. One of its two interior opposite angles is 59°. What is the other one (in degrees)?
  23. 23.In a right-angled triangle, one of the other two angles is 39°. What is the third angle (in degrees)?
  24. 24.In a right-angled triangle, one of the other two angles is 50°. What is the third angle (in degrees)?
  25. 25.Can a triangle have sides of 24 cm, 11 cm and 9 cm? (a) No (b) Yes
  26. 26.Can a triangle have sides of 12 cm, 4 cm and 17 cm? (a) No (b) Yes
  27. 27.Can a triangle have sides of 10 cm, 20 cm and 8 cm? (a) Yes (b) No
  28. 28.In triangle ABC, angle A = 48° and angle B = 60°. What is angle C (in degrees)?
  29. 29.In triangle ABC, angle A = 60° and angle B = 76°. What is angle C (in degrees)?
  30. 30.The longest side of a right-angled triangle is 20 cm and one of the other sides is 12 cm. How long is the third side (in cm)?
  31. 31.In an isosceles triangle, the angle between the two equal sides is 80°. What is each of the other two angles (in degrees)?
  32. 32.The angles of a triangle are in the ratio 3 : 3 : 4. What is the smallest angle (in degrees)?
  33. 33.In triangle ABC, angle A = 80° and angle B = 46°. What is angle C (in degrees)?
  34. 34.In triangle ABC, angle A = 98° and angle B = 22°. What is angle C (in degrees)?
  35. 35.In an isosceles triangle, the two equal angles are 65° each. What is the third angle (in degrees)?
  36. 36.In triangle ABC, angle A = 28° and angle B = 69°. What is angle C (in degrees)?
  37. 37.In a right-angled triangle, one of the other two angles is 15°. What is the third angle (in degrees)?
  38. 38.In triangle ABC, angle A = 73° and angle B = 24°. What is angle C (in degrees)?
  39. 39.The angles of a triangle are in the ratio 3 : 5 : 7. What is the biggest angle (in degrees)?
  40. 40.The angles of a triangle are in the ratio 2 : 3 : 5. What is the smallest angle (in degrees)?

Answer key

  1. 13
  2. 24
  3. 118
  4. 99
  5. 5
  6. 72
  7. 17
  8. 110
  9. 108
  10. 18
  11. 16
  12. 54
  13. 64
  14. 25
  15. 66
  16. 120
  17. Yes
  18. 90
  19. 80
  20. 66
  21. 22
  22. 64
  23. 51
  24. 40
  25. No
  26. No
  27. No
  28. 72
  29. 44
  30. 16
  31. 50
  32. 54
  33. 54
  34. 60
  35. 50
  36. 83
  37. 75
  38. 83
  39. 84
  40. 36

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