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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 786 · 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 a right-angled triangle, one of the other two angles is 51°. What is the third angle (in degrees)?
  2. 2.In a right-angled triangle, one of the other two angles is 12°. What is the third angle (in degrees)?
  3. 3.In an isosceles triangle, the two equal angles are 48° each. What is the third angle (in degrees)?
  4. 4.Can a triangle have sides of 6 cm, 10 cm and 10 cm? (a) No (b) Yes
  5. 5.In triangle ABC, angle A = 85° and angle B = 47°. What is angle C (in degrees)?
  6. 6.The angles of a triangle are in the ratio 2 : 3 : 5. What is the smallest angle (in degrees)?
  7. 7.An exterior angle of a triangle is 120°. One of its two interior opposite angles is 61°. What is the other one (in degrees)?
  8. 8.In an isosceles triangle, the angle between the two equal sides is 48°. What is each of the other two angles (in degrees)?
  9. 9.In triangle ABC, angle A = 32° and angle B = 21°. What is angle C (in degrees)?
  10. 10.The two shorter sides of a right-angled triangle are 20 cm and 15 cm. How long is the longest side (in cm)?
  11. 11.In triangle ABC, angle A = 75° and angle B = 35°. What is angle C (in degrees)?
  12. 12.The two interior opposite angles of a triangle are 23° and 32°. What is the exterior angle (in degrees)?
  13. 13.The angles of a triangle are in the ratio 1 : 2 : 3. What is the smallest angle (in degrees)?
  14. 14.In triangle ABC, angle A = 93° and angle B = 66°. What is angle C (in degrees)?
  15. 15.In triangle ABC, angle A = 22° and angle B = 86°. What is angle C (in degrees)?
  16. 16.In a right-angled triangle, one of the other two angles is 10°. What is the third angle (in degrees)?
  17. 17.The two interior opposite angles of a triangle are 73° and 61°. What is the exterior angle (in degrees)?
  18. 18.Can a triangle have sides of 16 cm, 11 cm and 9 cm? (a) No (b) Yes
  19. 19.The angles of a triangle are in the ratio 2 : 3 : 4. What is the smallest angle (in degrees)?
  20. 20.An exterior angle of a triangle is 101°. One of its two interior opposite angles is 55°. What is the other one (in degrees)?
  21. 21.In a right-angled triangle, one of the other two angles is 29°. What is the third angle (in degrees)?
  22. 22.In triangle ABC, angle A = 29° and angle B = 85°. What is angle C (in degrees)?
  23. 23.In triangle ABC, angle A = 96° and angle B = 51°. What is angle C (in degrees)?
  24. 24.In an isosceles triangle, the two equal angles are 74° each. What is the third angle (in degrees)?
  25. 25.An exterior angle of a triangle is 134°. One of its two interior opposite angles is 66°. What is the other one (in degrees)?
  26. 26.In a right-angled triangle, one of the other two angles is 16°. What is the third angle (in degrees)?
  27. 27.The angles of a triangle are in the ratio 1 : 4 : 5. What is the biggest angle (in degrees)?
  28. 28.In a right-angled triangle, one of the other two angles is 36°. What is the third angle (in degrees)?
  29. 29.Can a triangle have sides of 10 cm, 4 cm and 10 cm? (a) No (b) Yes
  30. 30.In a right-angled triangle, one of the other two angles is 64°. What is the third angle (in degrees)?
  31. 31.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)?
  32. 32.The angles of a triangle are in the ratio 1 : 3 : 5. What is the smallest angle (in degrees)?
  33. 33.In triangle ABC, angle A = 89° and angle B = 67°. What is angle C (in degrees)?
  34. 34.In triangle ABC, angle A = 24° and angle B = 92°. What is angle C (in degrees)?
  35. 35.In a right-angled triangle, one of the other two angles is 80°. What is the third angle (in degrees)?
  36. 36.In a right-angled triangle, one of the other two angles is 54°. What is the third angle (in degrees)?
  37. 37.In triangle ABC, angle A = 55° and angle B = 67°. What is angle C (in degrees)?
  38. 38.In triangle ABC, angle A = 80° and angle B = 66°. What is angle C (in degrees)?
  39. 39.The two shorter sides of a right-angled triangle are 12 cm and 9 cm. How long is the longest side (in cm)?
  40. 40.The angles of a triangle are in the ratio 1 : 1 : 2. What is the smallest angle (in degrees)?

Answer key

  1. 39
  2. 78
  3. 84
  4. Yes
  5. 48
  6. 36
  7. 59
  8. 66
  9. 127
  10. 25
  11. 70
  12. 55
  13. 30
  14. 21
  15. 72
  16. 80
  17. 134
  18. Yes
  19. 40
  20. 46
  21. 61
  22. 66
  23. 33
  24. 32
  25. 68
  26. 74
  27. 90
  28. 54
  29. Yes
  30. 26
  31. 24
  32. 20
  33. 24
  34. 64
  35. 10
  36. 36
  37. 58
  38. 34
  39. 15
  40. 45

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