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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 9 · 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 69° each. What is the third angle (in degrees)?
  2. 2.In an isosceles triangle, the two equal angles are 32° each. What is the third angle (in degrees)?
  3. 3.In an isosceles triangle, the angle between the two equal sides is 86°. What is each of the other two angles (in degrees)?
  4. 4.The two interior opposite angles of a triangle are 54° and 20°. What is the exterior angle (in degrees)?
  5. 5.In triangle ABC, angle A = 59° and angle B = 29°. What is angle C (in degrees)?
  6. 6.The angles of a triangle are in the ratio 5 : 6 : 7. What is the biggest angle (in degrees)?
  7. 7.In an isosceles triangle, the angle between the two equal sides is 20°. What is each of the other two angles (in degrees)?
  8. 8.In a right-angled triangle, one of the other two angles is 80°. What is the third angle (in degrees)?
  9. 9.In triangle ABC, angle A = 57° and angle B = 38°. What is angle C (in degrees)?
  10. 10.In a right-angled triangle, one of the other two angles is 26°. What is the third angle (in degrees)?
  11. 11.In an isosceles triangle, the angle between the two equal sides is 98°. What is each of the other two angles (in degrees)?
  12. 12.In a right-angled triangle, one of the other two angles is 77°. What is the third angle (in degrees)?
  13. 13.Can a triangle have sides of 8 cm, 8 cm and 20 cm? (a) No (b) Yes
  14. 14.In triangle ABC, angle A = 40° and angle B = 64°. What is angle C (in degrees)?
  15. 15.The two interior opposite angles of a triangle are 58° and 36°. What is the exterior angle (in degrees)?
  16. 16.An exterior angle of a triangle is 92°. One of its two interior opposite angles is 66°. What is the other one (in degrees)?
  17. 17.In triangle ABC, angle A = 61° and angle B = 37°. What is angle C (in degrees)?
  18. 18.In an isosceles triangle, the angle between the two equal sides is 28°. What is each of the other two angles (in degrees)?
  19. 19.The two shorter sides of a right-angled triangle are 24 cm and 7 cm. How long is the longest side (in cm)?
  20. 20.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)?
  21. 21.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)?
  22. 22.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)?
  23. 23.In triangle ABC, angle A = 53° and angle B = 37°. What is angle C (in degrees)?
  24. 24.Can a triangle have sides of 19 cm, 8 cm and 6 cm? (a) No (b) Yes
  25. 25.In triangle ABC, angle A = 66° and angle B = 22°. What is angle C (in degrees)?
  26. 26.The two shorter sides of a right-angled triangle are 24 cm and 18 cm. How long is the longest side (in cm)?
  27. 27.The longest side of a right-angled triangle is 39 cm and one of the other sides is 15 cm. How long is the third side (in cm)?
  28. 28.Can a triangle have sides of 2 cm, 3 cm and 2 cm? (a) No (b) Yes
  29. 29.In a right-angled triangle, one of the other two angles is 18°. What is the third angle (in degrees)?
  30. 30.The angles of a triangle are in the ratio 1 : 2 : 3. What is the smallest angle (in degrees)?
  31. 31.Can a triangle have sides of 12 cm, 5 cm and 4 cm? (a) No (b) Yes
  32. 32.The two shorter sides of a right-angled triangle are 6 cm and 8 cm. How long is the longest side (in cm)?
  33. 33.In triangle ABC, angle A = 76° and angle B = 28°. What is angle C (in degrees)?
  34. 34.The angles of a triangle are in the ratio 3 : 3 : 4. What is the biggest angle (in degrees)?
  35. 35.Can a triangle have sides of 17 cm, 8 cm and 7 cm? (a) No (b) Yes
  36. 36.In an isosceles triangle, the two equal angles are 66° each. What is the third angle (in degrees)?
  37. 37.In triangle ABC, angle A = 38° and angle B = 107°. What is angle C (in degrees)?
  38. 38.In an isosceles triangle, the two equal angles are 43° each. What is the third angle (in degrees)?
  39. 39.In triangle ABC, angle A = 57° and angle B = 76°. What is angle C (in degrees)?
  40. 40.An exterior angle of a triangle is 103°. One of its two interior opposite angles is 52°. What is the other one (in degrees)?

Answer key

  1. 42
  2. 116
  3. 47
  4. 74
  5. 92
  6. 70
  7. 80
  8. 10
  9. 85
  10. 64
  11. 41
  12. 13
  13. No
  14. 76
  15. 94
  16. 26
  17. 82
  18. 76
  19. 25
  20. 18
  21. 16
  22. 15
  23. 90
  24. No
  25. 92
  26. 30
  27. 36
  28. Yes
  29. 72
  30. 30
  31. No
  32. 10
  33. 76
  34. 72
  35. No
  36. 48
  37. 35
  38. 94
  39. 47
  40. 51

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