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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 125 · 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.The longest side of a right-angled triangle is 30 cm and one of the other sides is 24 cm. How long is the third side (in cm)?
  2. 2.The angles of a triangle are in the ratio 3 : 3 : 4. What is the biggest angle (in degrees)?
  3. 3.The angles of a triangle are in the ratio 4 : 5 : 6. What is the biggest angle (in degrees)?
  4. 4.In an isosceles triangle, the two equal angles are 35° each. What is the third angle (in degrees)?
  5. 5.In a right-angled triangle, one of the other two angles is 25°. What is the third angle (in degrees)?
  6. 6.Can a triangle have sides of 4 cm, 2 cm and 5 cm? (a) Yes (b) No
  7. 7.Can a triangle have sides of 9 cm, 4 cm and 10 cm? (a) No (b) Yes
  8. 8.The angles of a triangle are in the ratio 1 : 1 : 2. What is the biggest angle (in degrees)?
  9. 9.In a right-angled triangle, one of the other two angles is 30°. What is the third angle (in degrees)?
  10. 10.In an isosceles triangle, the angle between the two equal sides is 20°. What is each of the other two angles (in degrees)?
  11. 11.In triangle ABC, angle A = 33° and angle B = 73°. What is angle C (in degrees)?
  12. 12.In an isosceles triangle, the angle between the two equal sides is 28°. What is each of the other two angles (in degrees)?
  13. 13.Can a triangle have sides of 9 cm, 6 cm and 4 cm? (a) No (b) Yes
  14. 14.The two interior opposite angles of a triangle are 69° and 52°. What is the exterior angle (in degrees)?
  15. 15.In an isosceles triangle, the two equal angles are 26° each. What is the third angle (in degrees)?
  16. 16.The angles of a triangle are in the ratio 2 : 3 : 5. What is the smallest angle (in degrees)?
  17. 17.In triangle ABC, angle A = 85° and angle B = 68°. What is angle C (in degrees)?
  18. 18.The angles of a triangle are in the ratio 2 : 7 : 9. What is the biggest angle (in degrees)?
  19. 19.The two interior opposite angles of a triangle are 80° and 54°. What is the exterior angle (in degrees)?
  20. 20.The angles of a triangle are in the ratio 3 : 4 : 5. What is the smallest angle (in degrees)?
  21. 21.In triangle ABC, angle A = 29° and angle B = 24°. What is angle C (in degrees)?
  22. 22.An exterior angle of a triangle is 77°. One of its two interior opposite angles is 34°. What is the other one (in degrees)?
  23. 23.In an isosceles triangle, the two equal angles are 41° each. What is the third angle (in degrees)?
  24. 24.An exterior angle of a triangle is 149°. One of its two interior opposite angles is 74°. What is the other one (in degrees)?
  25. 25.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)?
  26. 26.The angles of a triangle are in the ratio 3 : 5 : 7. What is the biggest angle (in degrees)?
  27. 27.In triangle ABC, angle A = 94° and angle B = 31°. What is angle C (in degrees)?
  28. 28.The angles of a triangle are in the ratio 5 : 6 : 7. What is the biggest angle (in degrees)?
  29. 29.Can a triangle have sides of 12 cm, 18 cm and 5 cm? (a) Yes (b) No
  30. 30.In triangle ABC, angle A = 94° and angle B = 64°. What is angle C (in degrees)?
  31. 31.In triangle ABC, angle A = 30° and angle B = 113°. What is angle C (in degrees)?
  32. 32.The longest side of a right-angled triangle is 30 cm and one of the other sides is 18 cm. How long is the third side (in cm)?
  33. 33.The angles of a triangle are in the ratio 1 : 2 : 6. What is the biggest angle (in degrees)?
  34. 34.The two interior opposite angles of a triangle are 25° and 37°. What is the exterior angle (in degrees)?
  35. 35.Can a triangle have sides of 8 cm, 13 cm and 12 cm? (a) No (b) Yes
  36. 36.Can a triangle have sides of 10 cm, 10 cm and 10 cm? (a) Yes (b) No
  37. 37.Can a triangle have sides of 4 cm, 5 cm and 4 cm? (a) No (b) Yes
  38. 38.An exterior angle of a triangle is 119°. One of its two interior opposite angles is 39°. What is the other one (in degrees)?
  39. 39.In triangle ABC, angle A = 100° and angle B = 35°. What is angle C (in degrees)?
  40. 40.In triangle ABC, angle A = 38° and angle B = 106°. What is angle C (in degrees)?

Answer key

  1. 18
  2. 72
  3. 72
  4. 110
  5. 65
  6. Yes
  7. Yes
  8. 90
  9. 60
  10. 80
  11. 74
  12. 76
  13. Yes
  14. 121
  15. 128
  16. 36
  17. 27
  18. 90
  19. 134
  20. 45
  21. 127
  22. 43
  23. 98
  24. 75
  25. 8
  26. 84
  27. 55
  28. 70
  29. No
  30. 22
  31. 37
  32. 24
  33. 120
  34. 62
  35. Yes
  36. Yes
  37. Yes
  38. 80
  39. 45
  40. 36

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