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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 71 · 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 = 30° and angle B = 63°. What is angle C (in degrees)?
  2. 2.An exterior angle of a triangle is 80°. One of its two interior opposite angles is 28°. What is the other one (in degrees)?
  3. 3.The longest side of a right-angled triangle is 20 cm and one of the other sides is 12 cm. How long is the third side (in cm)?
  4. 4.An exterior angle of a triangle is 104°. One of its two interior opposite angles is 79°. What is the other one (in degrees)?
  5. 5.Can a triangle have sides of 2 cm, 9 cm and 9 cm? (a) No (b) Yes
  6. 6.The two interior opposite angles of a triangle are 32° and 79°. What is the exterior angle (in degrees)?
  7. 7.In triangle ABC, angle A = 33° and angle B = 75°. What is angle C (in degrees)?
  8. 8.In an isosceles triangle, the two equal angles are 69° each. What is the third angle (in degrees)?
  9. 9.The two interior opposite angles of a triangle are 72° and 77°. What is the exterior angle (in degrees)?
  10. 10.In triangle ABC, angle A = 90° and angle B = 44°. What is angle C (in degrees)?
  11. 11.Can a triangle have sides of 2 cm, 5 cm and 5 cm? (a) Yes (b) No
  12. 12.In a right-angled triangle, one of the other two angles is 48°. What is the third angle (in degrees)?
  13. 13.The angles of a triangle are in the ratio 3 : 5 : 7. What is the biggest angle (in degrees)?
  14. 14.The angles of a triangle are in the ratio 2 : 2 : 5. What is the biggest angle (in degrees)?
  15. 15.The two interior opposite angles of a triangle are 80° and 57°. What is the exterior angle (in degrees)?
  16. 16.The angles of a triangle are in the ratio 3 : 5 : 7. What is the smallest 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.In an isosceles triangle, the angle between the two equal sides is 140°. What is each of the other two angles (in degrees)?
  19. 19.The angles of a triangle are in the ratio 2 : 3 : 4. What is the biggest angle (in degrees)?
  20. 20.In a right-angled triangle, one of the other two angles is 12°. What is the third angle (in degrees)?
  21. 21.In an isosceles triangle, the angle between the two equal sides is 36°. What is each of the other two angles (in degrees)?
  22. 22.In triangle ABC, angle A = 23° and angle B = 81°. What is angle C (in degrees)?
  23. 23.In triangle ABC, angle A = 21° and angle B = 99°. What is angle C (in degrees)?
  24. 24.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)?
  25. 25.In triangle ABC, angle A = 99° and angle B = 28°. What is angle C (in degrees)?
  26. 26.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)?
  27. 27.In a right-angled triangle, one of the other two angles is 68°. What is the third angle (in degrees)?
  28. 28.An exterior angle of a triangle is 100°. One of its two interior opposite angles is 35°. What is the other one (in degrees)?
  29. 29.In an isosceles triangle, the angle between the two equal sides is 156°. What is each of the other two angles (in degrees)?
  30. 30.In a right-angled triangle, one of the other two angles is 43°. What is the third angle (in degrees)?
  31. 31.The angles of a triangle are in the ratio 1 : 2 : 2. What is the smallest angle (in degrees)?
  32. 32.An exterior angle of a triangle is 103°. One of its two interior opposite angles is 24°. What is the other one (in degrees)?
  33. 33.An exterior angle of a triangle is 89°. One of its two interior opposite angles is 33°. What is the other one (in degrees)?
  34. 34.In a right-angled triangle, one of the other two angles is 38°. What is the third angle (in degrees)?
  35. 35.In triangle ABC, angle A = 93° and angle B = 65°. What is angle C (in degrees)?
  36. 36.Can a triangle have sides of 8 cm, 11 cm and 19 cm? (a) No (b) Yes
  37. 37.The angles of a triangle are in the ratio 2 : 7 : 9. What is the biggest angle (in degrees)?
  38. 38.In a right-angled triangle, one of the other two angles is 75°. What is the third angle (in degrees)?
  39. 39.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)?
  40. 40.The two shorter sides of a right-angled triangle are 15 cm and 20 cm. How long is the longest side (in cm)?

Answer key

  1. 87
  2. 52
  3. 16
  4. 25
  5. Yes
  6. 111
  7. 72
  8. 42
  9. 149
  10. 46
  11. Yes
  12. 42
  13. 84
  14. 100
  15. 137
  16. 36
  17. 51
  18. 20
  19. 80
  20. 78
  21. 72
  22. 76
  23. 60
  24. 15
  25. 53
  26. 24
  27. 22
  28. 65
  29. 12
  30. 47
  31. 36
  32. 79
  33. 56
  34. 52
  35. 22
  36. No
  37. 90
  38. 15
  39. 8
  40. 25

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