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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 62 · 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.An exterior angle of a triangle is 111°. One of its two interior opposite angles is 69°. What is the other one (in degrees)?
  2. 2.In a right-angled triangle, one of the other two angles is 12°. What is the third angle (in degrees)?
  3. 3.In an isosceles triangle, the angle between the two equal sides is 80°. What is each of the other two angles (in degrees)?
  4. 4.The angles of a triangle are in the ratio 1 : 2 : 2. What is the smallest angle (in degrees)?
  5. 5.The angles of a triangle are in the ratio 1 : 2 : 2. What is the biggest angle (in degrees)?
  6. 6.An exterior angle of a triangle is 70°. One of its two interior opposite angles is 23°. What is the other one (in degrees)?
  7. 7.An exterior angle of a triangle is 108°. One of its two interior opposite angles is 79°. What is the other one (in degrees)?
  8. 8.In a right-angled triangle, one of the other two angles is 15°. What is the third angle (in degrees)?
  9. 9.An exterior angle of a triangle is 131°. One of its two interior opposite angles is 70°. What is the other one (in degrees)?
  10. 10.An exterior angle of a triangle is 94°. One of its two interior opposite angles is 69°. What is the other one (in degrees)?
  11. 11.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)?
  12. 12.In triangle ABC, angle A = 72° and angle B = 35°. What is angle C (in degrees)?
  13. 13.Can a triangle have sides of 14 cm, 7 cm and 5 cm? (a) No (b) Yes
  14. 14.In a right-angled triangle, one of the other two angles is 10°. What is the third angle (in degrees)?
  15. 15.The angles of a triangle are in the ratio 3 : 3 : 4. What is the biggest angle (in degrees)?
  16. 16.Can a triangle have sides of 3 cm, 20 cm and 12 cm? (a) Yes (b) No
  17. 17.In triangle ABC, angle A = 78° and angle B = 40°. What is angle C (in degrees)?
  18. 18.Can a triangle have sides of 12 cm, 22 cm and 10 cm? (a) No (b) Yes
  19. 19.In a right-angled triangle, one of the other two angles is 75°. What is the third angle (in degrees)?
  20. 20.Can a triangle have sides of 12 cm, 21 cm and 9 cm? (a) Yes (b) No
  21. 21.An exterior angle of a triangle is 100°. One of its two interior opposite angles is 47°. What is the other one (in degrees)?
  22. 22.The two interior opposite angles of a triangle are 45° and 43°. What is the exterior angle (in degrees)?
  23. 23.The two shorter sides of a right-angled triangle are 4 cm and 3 cm. How long is the longest side (in cm)?
  24. 24.Can a triangle have sides of 9 cm, 18 cm and 9 cm? (a) Yes (b) No
  25. 25.In triangle ABC, angle A = 82° and angle B = 25°. What is angle C (in degrees)?
  26. 26.In a right-angled triangle, one of the other two angles is 54°. What is the third angle (in degrees)?
  27. 27.The angles of a triangle are in the ratio 3 : 4 : 5. What is the biggest angle (in degrees)?
  28. 28.In a right-angled triangle, one of the other two angles is 38°. What is the third angle (in degrees)?
  29. 29.In an isosceles triangle, the two equal angles are 27° each. What is the third angle (in degrees)?
  30. 30.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)?
  31. 31.The two interior opposite angles of a triangle are 80° and 64°. What is the exterior angle (in degrees)?
  32. 32.An exterior angle of a triangle is 100°. One of its two interior opposite angles is 48°. What is the other one (in degrees)?
  33. 33.In triangle ABC, angle A = 35° and angle B = 86°. What is angle C (in degrees)?
  34. 34.In an isosceles triangle, the two equal angles are 70° each. What is the third angle (in degrees)?
  35. 35.In an isosceles triangle, the two equal angles are 26° each. What is the third angle (in degrees)?
  36. 36.The angles of a triangle are in the ratio 1 : 2 : 6. What is the biggest angle (in degrees)?
  37. 37.In triangle ABC, angle A = 60° and angle B = 60°. What is angle C (in degrees)?
  38. 38.In an isosceles triangle, the two equal angles are 36° each. What is the third angle (in degrees)?
  39. 39.The two interior opposite angles of a triangle are 49° and 41°. What is the exterior angle (in degrees)?
  40. 40.Can a triangle have sides of 7 cm, 14 cm and 7 cm? (a) Yes (b) No

Answer key

  1. 42
  2. 78
  3. 50
  4. 36
  5. 72
  6. 47
  7. 29
  8. 75
  9. 61
  10. 25
  11. 15
  12. 73
  13. No
  14. 80
  15. 72
  16. No
  17. 62
  18. No
  19. 15
  20. No
  21. 53
  22. 88
  23. 5
  24. No
  25. 73
  26. 36
  27. 75
  28. 52
  29. 126
  30. 7
  31. 144
  32. 52
  33. 59
  34. 40
  35. 128
  36. 120
  37. 60
  38. 108
  39. 90
  40. No

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