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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 825 · 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.Can a triangle have sides of 3 cm, 13 cm and 9 cm? (a) No (b) Yes
  2. 2.In triangle ABC, angle A = 50° and angle B = 22°. What is angle C (in degrees)?
  3. 3.The angles of a triangle are in the ratio 2 : 3 : 5. What is the smallest angle (in degrees)?
  4. 4.The angles of a triangle are in the ratio 1 : 3 : 5. What is the biggest angle (in degrees)?
  5. 5.Can a triangle have sides of 8 cm, 20 cm and 12 cm? (a) Yes (b) No
  6. 6.In triangle ABC, angle A = 67° and angle B = 53°. What is angle C (in degrees)?
  7. 7.In triangle ABC, angle A = 53° and angle B = 28°. What is angle C (in degrees)?
  8. 8.In a right-angled triangle, one of the other two angles is 68°. What is the third angle (in degrees)?
  9. 9.An exterior angle of a triangle is 110°. One of its two interior opposite angles is 58°. What is the other one (in degrees)?
  10. 10.Can a triangle have sides of 8 cm, 6 cm and 8 cm? (a) Yes (b) No
  11. 11.Can a triangle have sides of 9 cm, 15 cm and 6 cm? (a) Yes (b) No
  12. 12.In an isosceles triangle, the angle between the two equal sides is 140°. What is each of the other two angles (in degrees)?
  13. 13.In an isosceles triangle, the two equal angles are 69° each. What is the third angle (in degrees)?
  14. 14.The angles of a triangle are in the ratio 4 : 5 : 6. What is the biggest angle (in degrees)?
  15. 15.In triangle ABC, angle A = 51° and angle B = 81°. What is angle C (in degrees)?
  16. 16.In triangle ABC, angle A = 38° and angle B = 59°. What is angle C (in degrees)?
  17. 17.In a right-angled triangle, one of the other two angles is 39°. What is the third angle (in degrees)?
  18. 18.The angles of a triangle are in the ratio 1 : 2 : 2. What is the smallest angle (in degrees)?
  19. 19.In a right-angled triangle, one of the other two angles is 17°. What is the third angle (in degrees)?
  20. 20.An exterior angle of a triangle is 75°. One of its two interior opposite angles is 52°. What is the other one (in degrees)?
  21. 21.Can a triangle have sides of 21 cm, 9 cm and 10 cm? (a) No (b) Yes
  22. 22.In triangle ABC, angle A = 23° and angle B = 91°. What is angle C (in degrees)?
  23. 23.The angles of a triangle are in the ratio 2 : 3 : 4. What is the biggest angle (in degrees)?
  24. 24.In an isosceles triangle, the two equal angles are 76° each. What is the third angle (in degrees)?
  25. 25.Can a triangle have sides of 2 cm, 11 cm and 16 cm? (a) No (b) Yes
  26. 26.The two shorter sides of a right-angled triangle are 15 cm and 8 cm. How long is the longest side (in cm)?
  27. 27.In an isosceles triangle, the angle between the two equal sides is 72°. What is each of the other two angles (in degrees)?
  28. 28.The two interior opposite angles of a triangle are 37° and 72°. What is the exterior angle (in degrees)?
  29. 29.The two interior opposite angles of a triangle are 66° and 46°. What is the exterior angle (in degrees)?
  30. 30.In an isosceles triangle, the angle between the two equal sides is 138°. What is each of the other two angles (in degrees)?
  31. 31.In triangle ABC, angle A = 78° and angle B = 30°. What is angle C (in degrees)?
  32. 32.Can a triangle have sides of 2 cm, 7 cm and 4 cm? (a) No (b) Yes
  33. 33.The angles of a triangle are in the ratio 2 : 7 : 9. What is the smallest angle (in degrees)?
  34. 34.In a right-angled triangle, one of the other two angles is 41°. What is the third angle (in degrees)?
  35. 35.An exterior angle of a triangle is 129°. One of its two interior opposite angles is 78°. What is the other one (in degrees)?
  36. 36.Can a triangle have sides of 7 cm, 17 cm and 11 cm? (a) No (b) Yes
  37. 37.In a right-angled triangle, one of the other two angles is 62°. What is the third angle (in degrees)?
  38. 38.In triangle ABC, angle A = 87° and angle B = 70°. What is angle C (in degrees)?
  39. 39.Can a triangle have sides of 5 cm, 10 cm and 5 cm? (a) Yes (b) No
  40. 40.In a right-angled triangle, one of the other two angles is 80°. What is the third angle (in degrees)?

Answer key

  1. No
  2. 108
  3. 36
  4. 100
  5. No
  6. 60
  7. 99
  8. 22
  9. 52
  10. Yes
  11. No
  12. 20
  13. 42
  14. 72
  15. 48
  16. 83
  17. 51
  18. 36
  19. 73
  20. 23
  21. No
  22. 66
  23. 80
  24. 28
  25. No
  26. 17
  27. 54
  28. 109
  29. 112
  30. 21
  31. 72
  32. No
  33. 20
  34. 49
  35. 51
  36. Yes
  37. 28
  38. 23
  39. No
  40. 10

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