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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 401 · 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 = 21° and angle B = 69°. What is angle C (in degrees)?
  2. 2.In triangle ABC, angle A = 52° and angle B = 87°. What is angle C (in degrees)?
  3. 3.The angles of a triangle are in the ratio 1 : 2 : 3. What is the smallest angle (in degrees)?
  4. 4.The two interior opposite angles of a triangle are 67° and 23°. What is the exterior angle (in degrees)?
  5. 5.In triangle ABC, angle A = 85° and angle B = 44°. What is angle C (in degrees)?
  6. 6.The angles of a triangle are in the ratio 3 : 5 : 7. What is the biggest angle (in degrees)?
  7. 7.In triangle ABC, angle A = 50° and angle B = 84°. What is angle C (in degrees)?
  8. 8.In triangle ABC, angle A = 35° and angle B = 66°. What is angle C (in degrees)?
  9. 9.In triangle ABC, angle A = 82° and angle B = 48°. What is angle C (in degrees)?
  10. 10.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)?
  11. 11.The longest side of a right-angled triangle is 13 cm and one of the other sides is 5 cm. How long is the third side (in cm)?
  12. 12.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)?
  13. 13.In a right-angled triangle, one of the other two angles is 10°. What is the third angle (in degrees)?
  14. 14.In a right-angled triangle, one of the other two angles is 28°. What is the third angle (in degrees)?
  15. 15.The angles of a triangle are in the ratio 1 : 1 : 2. What is the biggest angle (in degrees)?
  16. 16.In an isosceles triangle, the two equal angles are 76° each. What is the third angle (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 longest side of a right-angled triangle is 25 cm and one of the other sides is 7 cm. How long is the third side (in cm)?
  19. 19.In an isosceles triangle, the two equal angles are 67° each. What is the third angle (in degrees)?
  20. 20.The longest side of a right-angled triangle is 26 cm and one of the other sides is 24 cm. How long is the third side (in cm)?
  21. 21.In an isosceles triangle, the angle between the two equal sides is 90°. What is each of the other two angles (in degrees)?
  22. 22.An exterior angle of a triangle is 130°. One of its two interior opposite angles is 55°. What is the other one (in degrees)?
  23. 23.The two interior opposite angles of a triangle are 39° and 69°. What is the exterior angle (in degrees)?
  24. 24.In a right-angled triangle, one of the other two angles is 19°. What is the third angle (in degrees)?
  25. 25.In a right-angled triangle, one of the other two angles is 56°. What is the third angle (in degrees)?
  26. 26.The angles of a triangle are in the ratio 1 : 4 : 5. What is the biggest angle (in degrees)?
  27. 27.Can a triangle have sides of 12 cm, 9 cm and 24 cm? (a) Yes (b) No
  28. 28.In triangle ABC, angle A = 56° and angle B = 47°. What is angle C (in degrees)?
  29. 29.An exterior angle of a triangle is 81°. One of its two interior opposite angles is 31°. What is the other one (in degrees)?
  30. 30.Can a triangle have sides of 8 cm, 6 cm and 3 cm? (a) Yes (b) No
  31. 31.An exterior angle of a triangle is 69°. One of its two interior opposite angles is 47°. What is the other one (in degrees)?
  32. 32.The two shorter sides of a right-angled triangle are 7 cm and 24 cm. How long is the longest side (in cm)?
  33. 33.In an isosceles triangle, the two equal angles are 48° each. What is the third angle (in degrees)?
  34. 34.An exterior angle of a triangle is 157°. One of its two interior opposite angles is 78°. What is the other one (in degrees)?
  35. 35.In a right-angled triangle, one of the other two angles is 25°. What is the third angle (in degrees)?
  36. 36.The angles of a triangle are in the ratio 5 : 6 : 7. What is the biggest angle (in degrees)?
  37. 37.The angles of a triangle are in the ratio 1 : 2 : 6. What is the biggest angle (in degrees)?
  38. 38.In triangle ABC, angle A = 76° and angle B = 60°. What is angle C (in degrees)?
  39. 39.The longest side of a right-angled triangle is 20 cm and one of the other sides is 16 cm. How long is the third side (in cm)?
  40. 40.In an isosceles triangle, the angle between the two equal sides is 44°. What is each of the other two angles (in degrees)?

Answer key

  1. 90
  2. 41
  3. 30
  4. 90
  5. 51
  6. 84
  7. 46
  8. 79
  9. 50
  10. 18
  11. 12
  12. 8
  13. 80
  14. 62
  15. 90
  16. 28
  17. 51
  18. 24
  19. 46
  20. 10
  21. 45
  22. 75
  23. 108
  24. 71
  25. 34
  26. 90
  27. No
  28. 77
  29. 50
  30. Yes
  31. 22
  32. 25
  33. 84
  34. 79
  35. 65
  36. 70
  37. 120
  38. 44
  39. 12
  40. 68

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