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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 897 · 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 = 61° and angle B = 79°. What is angle C (in degrees)?
  2. 2.In a right-angled triangle, one of the other two angles is 33°. What is the third angle (in degrees)?
  3. 3.In triangle ABC, angle A = 20° and angle B = 127°. What is angle C (in degrees)?
  4. 4.The angles of a triangle are in the ratio 1 : 3 : 5. What is the biggest angle (in degrees)?
  5. 5.In an isosceles triangle, the angle between the two equal sides is 36°. What is each of the other two angles (in degrees)?
  6. 6.The two shorter sides of a right-angled triangle are 20 cm and 15 cm. How long is the longest side (in cm)?
  7. 7.In an isosceles triangle, the angle between the two equal sides is 32°. What is each of the other two angles (in degrees)?
  8. 8.In triangle ABC, angle A = 86° and angle B = 62°. What is angle C (in degrees)?
  9. 9.In an isosceles triangle, the two equal angles are 51° each. What is the third angle (in degrees)?
  10. 10.The two shorter sides of a right-angled triangle are 6 cm and 8 cm. How long is the longest side (in cm)?
  11. 11.An exterior angle of a triangle is 91°. One of its two interior opposite angles is 58°. What is the other one (in degrees)?
  12. 12.In triangle ABC, angle A = 76° and angle B = 68°. What is angle C (in degrees)?
  13. 13.The two interior opposite angles of a triangle are 22° and 62°. What is the exterior angle (in degrees)?
  14. 14.In triangle ABC, angle A = 92° and angle B = 21°. What is angle C (in degrees)?
  15. 15.The angles of a triangle are in the ratio 1 : 4 : 5. What is the smallest angle (in degrees)?
  16. 16.In an isosceles triangle, the two equal angles are 77° each. What is the third angle (in degrees)?
  17. 17.The angles of a triangle are in the ratio 1 : 2 : 6. What is the smallest angle (in degrees)?
  18. 18.In an isosceles triangle, the two equal angles are 38° each. What is the third angle (in degrees)?
  19. 19.In a right-angled triangle, one of the other two angles is 47°. What is the third angle (in degrees)?
  20. 20.An exterior angle of a triangle is 92°. One of its two interior opposite angles is 22°. What is the other one (in degrees)?
  21. 21.In a right-angled triangle, one of the other two angles is 40°. What is the third angle (in degrees)?
  22. 22.In a right-angled triangle, one of the other two angles is 25°. What is the third angle (in degrees)?
  23. 23.In an isosceles triangle, the two equal angles are 78° each. What is the third angle (in degrees)?
  24. 24.The angles of a triangle are in the ratio 1 : 4 : 5. What is the biggest angle (in degrees)?
  25. 25.In a right-angled triangle, one of the other two angles is 16°. What is the third angle (in degrees)?
  26. 26.In an isosceles triangle, the two equal angles are 53° each. What is the third angle (in degrees)?
  27. 27.The two shorter sides of a right-angled triangle are 12 cm and 16 cm. How long is the longest side (in cm)?
  28. 28.The two interior opposite angles of a triangle are 30° and 29°. What is the exterior angle (in degrees)?
  29. 29.The angles of a triangle are in the ratio 1 : 2 : 2. What is the smallest angle (in degrees)?
  30. 30.In a right-angled triangle, one of the other two angles is 51°. What is the third angle (in degrees)?
  31. 31.The angles of a triangle are in the ratio 2 : 7 : 9. What is the biggest angle (in degrees)?
  32. 32.The two interior opposite angles of a triangle are 31° and 48°. What is the exterior angle (in degrees)?
  33. 33.In an isosceles triangle, the two equal angles are 76° each. What is the third angle (in degrees)?
  34. 34.The angles of a triangle are in the ratio 1 : 2 : 3. What is the biggest angle (in degrees)?
  35. 35.In an isosceles triangle, the angle between the two equal sides is 48°. What is each of the other two angles (in degrees)?
  36. 36.The angles of a triangle are in the ratio 2 : 2 : 5. What is the biggest angle (in degrees)?
  37. 37.In an isosceles triangle, the angle between the two equal sides is 126°. What is each of the other two angles (in degrees)?
  38. 38.The longest side of a right-angled triangle is 30 cm and one of the other sides is 18 cm. How long is the third side (in cm)?
  39. 39.In triangle ABC, angle A = 85° and angle B = 30°. What is angle C (in degrees)?
  40. 40.Can a triangle have sides of 2 cm, 4 cm and 4 cm? (a) Yes (b) No

Answer key

  1. 40
  2. 57
  3. 33
  4. 100
  5. 72
  6. 25
  7. 74
  8. 32
  9. 78
  10. 10
  11. 33
  12. 36
  13. 84
  14. 67
  15. 18
  16. 26
  17. 20
  18. 104
  19. 43
  20. 70
  21. 50
  22. 65
  23. 24
  24. 90
  25. 74
  26. 74
  27. 20
  28. 59
  29. 36
  30. 39
  31. 90
  32. 79
  33. 28
  34. 90
  35. 66
  36. 100
  37. 27
  38. 24
  39. 65
  40. Yes

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