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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 256 · 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 triangle ABC, angle A = 73° and angle B = 23°. What is angle C (in degrees)?
  2. 2.In a right-angled triangle, one of the other two angles is 45°. What is the third angle (in degrees)?
  3. 3.In a right-angled triangle, one of the other two angles is 55°. What is the third angle (in degrees)?
  4. 4.In an isosceles triangle, the angle between the two equal sides is 50°. What is each of the other two angles (in degrees)?
  5. 5.The longest side of a right-angled triangle is 5 cm and one of the other sides is 4 cm. How long is the third side (in cm)?
  6. 6.An exterior angle of a triangle is 67°. One of its two interior opposite angles is 28°. What is the other one (in degrees)?
  7. 7.In a right-angled triangle, one of the other two angles is 12°. What is the third angle (in degrees)?
  8. 8.In a right-angled triangle, one of the other two angles is 31°. What is the third angle (in degrees)?
  9. 9.The angles of a triangle are in the ratio 1 : 2 : 3. What is the biggest angle (in degrees)?
  10. 10.In triangle ABC, angle A = 33° and angle B = 25°. What is angle C (in degrees)?
  11. 11.The two shorter sides of a right-angled triangle are 10 cm and 24 cm. How long is the longest side (in cm)?
  12. 12.In triangle ABC, angle A = 53° and angle B = 47°. What is angle C (in degrees)?
  13. 13.The angles of a triangle are in the ratio 2 : 2 : 5. What is the biggest angle (in degrees)?
  14. 14.In an isosceles triangle, the angle between the two equal sides is 44°. What is each of the other two angles (in degrees)?
  15. 15.An exterior angle of a triangle is 100°. One of its two interior opposite angles is 28°. What is the other one (in degrees)?
  16. 16.The two interior opposite angles of a triangle are 32° and 47°. What is the exterior angle (in degrees)?
  17. 17.The angles of a triangle are in the ratio 4 : 5 : 6. What is the biggest angle (in degrees)?
  18. 18.The two interior opposite angles of a triangle are 20° and 58°. What is the exterior angle (in degrees)?
  19. 19.Can a triangle have sides of 5 cm, 2 cm and 4 cm? (a) No (b) Yes
  20. 20.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)?
  21. 21.Can a triangle have sides of 9 cm, 2 cm and 4 cm? (a) No (b) Yes
  22. 22.Can a triangle have sides of 6 cm, 18 cm and 11 cm? (a) Yes (b) No
  23. 23.The two interior opposite angles of a triangle are 69° and 37°. What is the exterior angle (in degrees)?
  24. 24.The two interior opposite angles of a triangle are 55° and 68°. What is the exterior angle (in degrees)?
  25. 25.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)?
  26. 26.The two interior opposite angles of a triangle are 36° and 36°. What is the exterior angle (in degrees)?
  27. 27.Can a triangle have sides of 11 cm, 5 cm and 8 cm? (a) No (b) Yes
  28. 28.The two interior opposite angles of a triangle are 44° and 31°. What is the exterior angle (in degrees)?
  29. 29.The angles of a triangle are in the ratio 3 : 4 : 5. What is the smallest angle (in degrees)?
  30. 30.In triangle ABC, angle A = 48° and angle B = 67°. What is angle C (in degrees)?
  31. 31.In an isosceles triangle, the two equal angles are 29° each. What is the third angle (in degrees)?
  32. 32.The angles of a triangle are in the ratio 3 : 5 : 7. What is the biggest angle (in degrees)?
  33. 33.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)?
  34. 34.Can a triangle have sides of 10 cm, 17 cm and 3 cm? (a) Yes (b) No
  35. 35.In triangle ABC, angle A = 50° and angle B = 44°. What is angle C (in degrees)?
  36. 36.In triangle ABC, angle A = 25° and angle B = 34°. What is angle C (in degrees)?
  37. 37.An exterior angle of a triangle is 85°. One of its two interior opposite angles is 31°. What is the other one (in degrees)?
  38. 38.The angles of a triangle are in the ratio 1 : 1 : 2. What is the smallest angle (in degrees)?
  39. 39.In a right-angled triangle, one of the other two angles is 78°. What is the third angle (in degrees)?
  40. 40.In triangle ABC, angle A = 58° and angle B = 59°. What is angle C (in degrees)?

Answer key

  1. 84
  2. 45
  3. 35
  4. 65
  5. 3
  6. 39
  7. 78
  8. 59
  9. 90
  10. 122
  11. 26
  12. 80
  13. 100
  14. 68
  15. 72
  16. 79
  17. 72
  18. 78
  19. Yes
  20. 15
  21. No
  22. No
  23. 106
  24. 123
  25. 24
  26. 72
  27. Yes
  28. 75
  29. 45
  30. 65
  31. 122
  32. 84
  33. 18
  34. No
  35. 86
  36. 121
  37. 54
  38. 45
  39. 12
  40. 63

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