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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 484 · 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 a right-angled triangle, one of the other two angles is 21°. What is the third angle (in degrees)?
  2. 2.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)?
  3. 3.The angles of a triangle are in the ratio 1 : 3 : 5. What is the biggest angle (in degrees)?
  4. 4.Can a triangle have sides of 12 cm, 8 cm and 5 cm? (a) No (b) Yes
  5. 5.In a right-angled triangle, one of the other two angles is 23°. What is the third angle (in degrees)?
  6. 6.The longest side of a right-angled triangle is 13 cm and one of the other sides is 12 cm. How long is the third side (in cm)?
  7. 7.An exterior angle of a triangle is 98°. One of its two interior opposite angles is 34°. What is the other one (in degrees)?
  8. 8.In triangle ABC, angle A = 32° and angle B = 106°. What is angle C (in degrees)?
  9. 9.The two interior opposite angles of a triangle are 41° and 42°. What is the exterior angle (in degrees)?
  10. 10.The two shorter sides of a right-angled triangle are 5 cm and 12 cm. How long is the longest side (in cm)?
  11. 11.The angles of a triangle are in the ratio 5 : 6 : 7. What is the biggest angle (in degrees)?
  12. 12.Can a triangle have sides of 12 cm, 5 cm and 10 cm? (a) Yes (b) No
  13. 13.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)?
  14. 14.Can a triangle have sides of 8 cm, 8 cm and 10 cm? (a) No (b) Yes
  15. 15.In a right-angled triangle, one of the other two angles is 44°. What is the third angle (in degrees)?
  16. 16.In triangle ABC, angle A = 65° and angle B = 32°. What is angle C (in degrees)?
  17. 17.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)?
  18. 18.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)?
  19. 19.In triangle ABC, angle A = 82° and angle B = 24°. What is angle C (in degrees)?
  20. 20.Can a triangle have sides of 19 cm, 9 cm and 9 cm? (a) No (b) Yes
  21. 21.The angles of a triangle are in the ratio 2 : 2 : 5. What is the smallest angle (in degrees)?
  22. 22.Can a triangle have sides of 10 cm, 21 cm and 10 cm? (a) No (b) Yes
  23. 23.In triangle ABC, angle A = 28° and angle B = 114°. What is angle C (in degrees)?
  24. 24.The two shorter sides of a right-angled triangle are 12 cm and 9 cm. How long is the longest side (in cm)?
  25. 25.Can a triangle have sides of 12 cm, 18 cm and 5 cm? (a) Yes (b) No
  26. 26.An exterior angle of a triangle is 83°. One of its two interior opposite angles is 46°. What is the other one (in degrees)?
  27. 27.The two interior opposite angles of a triangle are 25° and 58°. What is the exterior angle (in degrees)?
  28. 28.The two shorter sides of a right-angled triangle are 15 cm and 8 cm. How long is the longest side (in cm)?
  29. 29.In an isosceles triangle, the angle between the two equal sides is 34°. What is each of the other two angles (in degrees)?
  30. 30.The angles of a triangle are in the ratio 5 : 6 : 7. What is the smallest angle (in degrees)?
  31. 31.The angles of a triangle are in the ratio 3 : 4 : 5. What is the biggest angle (in degrees)?
  32. 32.An exterior angle of a triangle is 61°. One of its two interior opposite angles is 37°. What is the other one (in degrees)?
  33. 33.In an isosceles triangle, the angle between the two equal sides is 126°. What is each of the other two angles (in degrees)?
  34. 34.In a right-angled triangle, one of the other two angles is 60°. What is the third angle (in degrees)?
  35. 35.The longest side of a right-angled triangle is 25 cm and one of the other sides is 24 cm. How long is the third side (in cm)?
  36. 36.The two interior opposite angles of a triangle are 30° and 53°. What is the exterior angle (in degrees)?
  37. 37.The two interior opposite angles of a triangle are 53° and 34°. What is the exterior angle (in degrees)?
  38. 38.In triangle ABC, angle A = 35° and angle B = 33°. What is angle C (in degrees)?
  39. 39.The two interior opposite angles of a triangle are 35° and 50°. What is the exterior angle (in degrees)?
  40. 40.In an isosceles triangle, the angle between the two equal sides is 78°. What is each of the other two angles (in degrees)?

Answer key

  1. 69
  2. 24
  3. 100
  4. Yes
  5. 67
  6. 5
  7. 64
  8. 42
  9. 83
  10. 13
  11. 70
  12. Yes
  13. 15
  14. Yes
  15. 46
  16. 83
  17. 10
  18. 3
  19. 74
  20. No
  21. 40
  22. No
  23. 38
  24. 15
  25. No
  26. 37
  27. 83
  28. 17
  29. 73
  30. 50
  31. 75
  32. 24
  33. 27
  34. 30
  35. 7
  36. 83
  37. 87
  38. 112
  39. 85
  40. 51

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