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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 709 · 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 = 51° and angle B = 78°. What is angle C (in degrees)?
  2. 2.In a right-angled triangle, one of the other two angles is 22°. What is the third angle (in degrees)?
  3. 3.The two shorter sides of a right-angled triangle are 15 cm and 20 cm. How long is the longest side (in cm)?
  4. 4.Can a triangle have sides of 3 cm, 5 cm and 8 cm? (a) Yes (b) No
  5. 5.An exterior angle of a triangle is 75°. One of its two interior opposite angles is 20°. What is the other one (in degrees)?
  6. 6.Can a triangle have sides of 8 cm, 5 cm and 6 cm? (a) Yes (b) No
  7. 7.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)?
  8. 8.In an isosceles triangle, the angle between the two equal sides is 142°. What is each of the other two angles (in degrees)?
  9. 9.In triangle ABC, angle A = 63° and angle B = 35°. What is angle C (in degrees)?
  10. 10.In an isosceles triangle, the two equal angles are 76° each. What is the third angle (in degrees)?
  11. 11.In triangle ABC, angle A = 41° and angle B = 57°. What is angle C (in degrees)?
  12. 12.In triangle ABC, angle A = 30° and angle B = 97°. What is angle C (in degrees)?
  13. 13.An exterior angle of a triangle is 142°. One of its two interior opposite angles is 78°. What is the other one (in degrees)?
  14. 14.Can a triangle have sides of 5 cm, 11 cm and 16 cm? (a) No (b) Yes
  15. 15.The longest side of a right-angled triangle is 15 cm and one of the other sides is 9 cm. How long is the third side (in cm)?
  16. 16.Can a triangle have sides of 9 cm, 14 cm and 8 cm? (a) Yes (b) No
  17. 17.The two shorter sides of a right-angled triangle are 15 cm and 8 cm. How long is the longest side (in cm)?
  18. 18.An exterior angle of a triangle is 108°. One of its two interior opposite angles is 49°. What is the other one (in degrees)?
  19. 19.The two interior opposite angles of a triangle are 79° and 63°. What is the exterior angle (in degrees)?
  20. 20.In a right-angled triangle, one of the other two angles is 68°. What is the third angle (in degrees)?
  21. 21.An exterior angle of a triangle is 112°. One of its two interior opposite angles is 80°. What is the other one (in degrees)?
  22. 22.The two interior opposite angles of a triangle are 55° and 24°. What is the exterior angle (in degrees)?
  23. 23.Can a triangle have sides of 8 cm, 11 cm and 5 cm? (a) No (b) Yes
  24. 24.Can a triangle have sides of 9 cm, 2 cm and 10 cm? (a) No (b) Yes
  25. 25.Can a triangle have sides of 10 cm, 9 cm and 10 cm? (a) Yes (b) No
  26. 26.The angles of a triangle are in the ratio 2 : 7 : 9. What is the biggest angle (in degrees)?
  27. 27.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)?
  28. 28.Can a triangle have sides of 9 cm, 15 cm and 5 cm? (a) Yes (b) No
  29. 29.Can a triangle have sides of 10 cm, 10 cm and 6 cm? (a) Yes (b) No
  30. 30.Can a triangle have sides of 3 cm, 3 cm and 6 cm? (a) Yes (b) No
  31. 31.Can a triangle have sides of 7 cm, 17 cm and 6 cm? (a) No (b) Yes
  32. 32.In a right-angled triangle, one of the other two angles is 12°. What is the third angle (in degrees)?
  33. 33.The two interior opposite angles of a triangle are 21° and 45°. What is the exterior angle (in degrees)?
  34. 34.In triangle ABC, angle A = 83° and angle B = 31°. What is angle C (in degrees)?
  35. 35.In triangle ABC, angle A = 85° and angle B = 22°. What is angle C (in degrees)?
  36. 36.In an isosceles triangle, the two equal angles are 66° each. What is the third angle (in degrees)?
  37. 37.In a right-angled triangle, one of the other two angles is 43°. What is the third angle (in degrees)?
  38. 38.The angles of a triangle are in the ratio 1 : 4 : 5. What is the smallest angle (in degrees)?
  39. 39.The longest side of a right-angled triangle is 10 cm and one of the other sides is 8 cm. How long is the third side (in cm)?
  40. 40.Can a triangle have sides of 5 cm, 8 cm and 2 cm? (a) No (b) Yes

Answer key

  1. 51
  2. 68
  3. 25
  4. No
  5. 55
  6. Yes
  7. 8
  8. 19
  9. 82
  10. 28
  11. 82
  12. 53
  13. 64
  14. No
  15. 12
  16. Yes
  17. 17
  18. 59
  19. 142
  20. 22
  21. 32
  22. 79
  23. Yes
  24. Yes
  25. Yes
  26. 90
  27. 24
  28. No
  29. Yes
  30. No
  31. No
  32. 78
  33. 66
  34. 66
  35. 73
  36. 48
  37. 47
  38. 18
  39. 6
  40. No

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