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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 263 · 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 = 28° and angle B = 72°. What is angle C (in degrees)?
  2. 2.In an isosceles triangle, the two equal angles are 56° each. What is the third angle (in degrees)?
  3. 3.The angles of a triangle are in the ratio 3 : 5 : 7. What is the biggest angle (in degrees)?
  4. 4.In a right-angled triangle, one of the other two angles is 22°. What is the third angle (in degrees)?
  5. 5.Can a triangle have sides of 5 cm, 9 cm and 15 cm? (a) No (b) Yes
  6. 6.The angles of a triangle are in the ratio 2 : 2 : 5. What is the smallest angle (in degrees)?
  7. 7.Can a triangle have sides of 10 cm, 10 cm and 16 cm? (a) Yes (b) No
  8. 8.In an isosceles triangle, the two equal angles are 51° each. What is the third angle (in degrees)?
  9. 9.In triangle ABC, angle A = 75° and angle B = 30°. What is angle C (in degrees)?
  10. 10.In an isosceles triangle, the angle between the two equal sides is 82°. What is each of the other two angles (in degrees)?
  11. 11.The angles of a triangle are in the ratio 1 : 2 : 3. What is the smallest angle (in degrees)?
  12. 12.In triangle ABC, angle A = 40° and angle B = 70°. What is angle C (in degrees)?
  13. 13.The angles of a triangle are in the ratio 1 : 3 : 5. What is the biggest angle (in degrees)?
  14. 14.In a right-angled triangle, one of the other two angles is 63°. What is the third angle (in degrees)?
  15. 15.In triangle ABC, angle A = 75° and angle B = 75°. What is angle C (in degrees)?
  16. 16.The two interior opposite angles of a triangle are 63° and 21°. What is the exterior angle (in degrees)?
  17. 17.The two interior opposite angles of a triangle are 26° and 74°. What is the exterior angle (in degrees)?
  18. 18.An exterior angle of a triangle is 77°. One of its two interior opposite angles is 56°. What is the other one (in degrees)?
  19. 19.In triangle ABC, angle A = 98° and angle B = 22°. What is angle C (in degrees)?
  20. 20.Can a triangle have sides of 2 cm, 8 cm and 9 cm? (a) No (b) Yes
  21. 21.In a right-angled triangle, one of the other two angles is 55°. What is the third angle (in degrees)?
  22. 22.In triangle ABC, angle A = 67° and angle B = 39°. What is angle C (in degrees)?
  23. 23.In an isosceles triangle, the two equal angles are 46° each. What is the third angle (in degrees)?
  24. 24.The two interior opposite angles of a triangle are 53° and 56°. What is the exterior angle (in degrees)?
  25. 25.In an isosceles triangle, the two equal angles are 47° each. What is the third angle (in degrees)?
  26. 26.An exterior angle of a triangle is 109°. One of its two interior opposite angles is 41°. What is the other one (in degrees)?
  27. 27.An exterior angle of a triangle is 113°. One of its two interior opposite angles is 38°. What is the other one (in degrees)?
  28. 28.The two interior opposite angles of a triangle are 64° and 68°. What is the exterior angle (in degrees)?
  29. 29.An exterior angle of a triangle is 70°. One of its two interior opposite angles is 34°. What is the other one (in degrees)?
  30. 30.The two shorter sides of a right-angled triangle are 7 cm and 24 cm. How long is the longest side (in cm)?
  31. 31.The angles of a triangle are in the ratio 2 : 3 : 5. What is the smallest angle (in degrees)?
  32. 32.In triangle ABC, angle A = 27° and angle B = 21°. What is angle C (in degrees)?
  33. 33.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)?
  34. 34.Can a triangle have sides of 9 cm, 10 cm and 14 cm? (a) No (b) Yes
  35. 35.The two shorter sides of a right-angled triangle are 8 cm and 15 cm. How long is the longest side (in cm)?
  36. 36.In triangle ABC, angle A = 50° and angle B = 75°. What is angle C (in degrees)?
  37. 37.In an isosceles triangle, the two equal angles are 63° each. What is the third angle (in degrees)?
  38. 38.An exterior angle of a triangle is 123°. One of its two interior opposite angles is 68°. What is the other one (in degrees)?
  39. 39.In triangle ABC, angle A = 34° and angle B = 40°. What is angle C (in degrees)?
  40. 40.The two interior opposite angles of a triangle are 73° and 71°. What is the exterior angle (in degrees)?

Answer key

  1. 80
  2. 68
  3. 84
  4. 68
  5. No
  6. 40
  7. Yes
  8. 78
  9. 75
  10. 49
  11. 30
  12. 70
  13. 100
  14. 27
  15. 30
  16. 84
  17. 100
  18. 21
  19. 60
  20. Yes
  21. 35
  22. 74
  23. 88
  24. 109
  25. 86
  26. 68
  27. 75
  28. 132
  29. 36
  30. 25
  31. 36
  32. 132
  33. 15
  34. Yes
  35. 17
  36. 55
  37. 54
  38. 55
  39. 106
  40. 144

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