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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 227 · 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 = 68° and angle B = 50°. What is angle C (in degrees)?
  2. 2.In a right-angled triangle, one of the other two angles is 13°. What is the third angle (in degrees)?
  3. 3.The angles of a triangle are in the ratio 3 : 3 : 4. What is the smallest angle (in degrees)?
  4. 4.In a right-angled triangle, one of the other two angles is 21°. What is the third angle (in degrees)?
  5. 5.The angles of a triangle are in the ratio 1 : 2 : 6. What is the biggest angle (in degrees)?
  6. 6.In a right-angled triangle, one of the other two angles is 74°. What is the third angle (in degrees)?
  7. 7.An exterior angle of a triangle is 108°. One of its two interior opposite angles is 74°. What is the other one (in degrees)?
  8. 8.An exterior angle of a triangle is 61°. One of its two interior opposite angles is 28°. What is the other one (in degrees)?
  9. 9.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)?
  10. 10.Can a triangle have sides of 16 cm, 6 cm and 6 cm? (a) Yes (b) No
  11. 11.In an isosceles triangle, the angle between the two equal sides is 118°. What is each of the other two angles (in degrees)?
  12. 12.In an isosceles triangle, the angle between the two equal sides is 50°. What is each of the other two angles (in degrees)?
  13. 13.In a right-angled triangle, one of the other two angles is 28°. What is the third angle (in degrees)?
  14. 14.In triangle ABC, angle A = 27° and angle B = 83°. What is angle C (in degrees)?
  15. 15.The angles of a triangle are in the ratio 1 : 4 : 5. What is the biggest angle (in degrees)?
  16. 16.In a right-angled triangle, one of the other two angles is 20°. What is the third angle (in degrees)?
  17. 17.In triangle ABC, angle A = 22° and angle B = 40°. What is angle C (in degrees)?
  18. 18.Can a triangle have sides of 14 cm, 4 cm and 9 cm? (a) Yes (b) No
  19. 19.In an isosceles triangle, the two equal angles are 65° each. What is the third angle (in degrees)?
  20. 20.The two interior opposite angles of a triangle are 55° and 62°. What is the exterior angle (in degrees)?
  21. 21.Can a triangle have sides of 2 cm, 9 cm and 13 cm? (a) No (b) Yes
  22. 22.The two shorter sides of a right-angled triangle are 12 cm and 5 cm. How long is the longest side (in cm)?
  23. 23.The two shorter sides of a right-angled triangle are 7 cm and 24 cm. How long is the longest side (in cm)?
  24. 24.Can a triangle have sides of 5 cm, 7 cm and 11 cm? (a) No (b) Yes
  25. 25.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)?
  26. 26.An exterior angle of a triangle is 101°. One of its two interior opposite angles is 73°. What is the other one (in degrees)?
  27. 27.In triangle ABC, angle A = 63° and angle B = 61°. What is angle C (in degrees)?
  28. 28.In a right-angled triangle, one of the other two angles is 49°. What is the third angle (in degrees)?
  29. 29.An exterior angle of a triangle is 116°. One of its two interior opposite angles is 39°. What is the other one (in degrees)?
  30. 30.In a right-angled triangle, one of the other two angles is 45°. What is the third angle (in degrees)?
  31. 31.The two interior opposite angles of a triangle are 28° and 53°. What is the exterior angle (in degrees)?
  32. 32.The two interior opposite angles of a triangle are 36° and 44°. What is the exterior angle (in degrees)?
  33. 33.In triangle ABC, angle A = 90° and angle B = 51°. What is angle C (in degrees)?
  34. 34.Can a triangle have sides of 9 cm, 5 cm and 6 cm? (a) No (b) Yes
  35. 35.In an isosceles triangle, the angle between the two equal sides is 36°. What is each of the other two angles (in degrees)?
  36. 36.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)?
  37. 37.In triangle ABC, angle A = 63° and angle B = 70°. What is angle C (in degrees)?
  38. 38.The angles of a triangle are in the ratio 1 : 2 : 2. What is the biggest angle (in degrees)?
  39. 39.In an isosceles triangle, the angle between the two equal sides is 160°. What is each of the other two angles (in degrees)?
  40. 40.In triangle ABC, angle A = 98° and angle B = 53°. What is angle C (in degrees)?

Answer key

  1. 62
  2. 77
  3. 54
  4. 69
  5. 120
  6. 16
  7. 34
  8. 33
  9. 8
  10. No
  11. 31
  12. 65
  13. 62
  14. 70
  15. 90
  16. 70
  17. 118
  18. No
  19. 50
  20. 117
  21. No
  22. 13
  23. 25
  24. Yes
  25. 12
  26. 28
  27. 56
  28. 41
  29. 77
  30. 45
  31. 81
  32. 80
  33. 39
  34. Yes
  35. 72
  36. 7
  37. 47
  38. 72
  39. 10
  40. 29

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