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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 757 · 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 = 27° and angle B = 80°. What is angle C (in degrees)?
  2. 2.In a right-angled triangle, one of the other two angles is 56°. What is the third angle (in degrees)?
  3. 3.In a right-angled triangle, one of the other two angles is 47°. What is the third angle (in degrees)?
  4. 4.In an isosceles triangle, the angle between the two equal sides is 84°. What is each of the other two angles (in degrees)?
  5. 5.In a right-angled triangle, one of the other two angles is 72°. What is the third angle (in degrees)?
  6. 6.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)?
  7. 7.The longest side of a right-angled triangle is 25 cm and one of the other sides is 20 cm. How long is the third side (in cm)?
  8. 8.In triangle ABC, angle A = 61° and angle B = 81°. What is angle C (in degrees)?
  9. 9.The two interior opposite angles of a triangle are 65° and 42°. What is the exterior angle (in degrees)?
  10. 10.Can a triangle have sides of 13 cm, 7 cm and 5 cm? (a) No (b) Yes
  11. 11.In an isosceles triangle, the angle between the two equal sides is 48°. 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 35°. What is the third angle (in degrees)?
  14. 14.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)?
  15. 15.Can a triangle have sides of 10 cm, 5 cm and 17 cm? (a) No (b) Yes
  16. 16.The two interior opposite angles of a triangle are 30° and 54°. What is the exterior angle (in degrees)?
  17. 17.An exterior angle of a triangle is 109°. One of its two interior opposite angles is 60°. What is the other one (in degrees)?
  18. 18.In triangle ABC, angle A = 45° and angle B = 28°. What is angle C (in degrees)?
  19. 19.The two interior opposite angles of a triangle are 26° and 77°. What is the exterior angle (in degrees)?
  20. 20.The angles of a triangle are in the ratio 1 : 4 : 5. What is the smallest angle (in degrees)?
  21. 21.In triangle ABC, angle A = 45° and angle B = 101°. What is angle C (in degrees)?
  22. 22.The angles of a triangle are in the ratio 1 : 2 : 2. What is the smallest angle (in degrees)?
  23. 23.The longest side of a right-angled triangle is 26 cm and one of the other sides is 10 cm. How long is the third side (in cm)?
  24. 24.Can a triangle have sides of 22 cm, 12 cm and 5 cm? (a) No (b) Yes
  25. 25.In triangle ABC, angle A = 90° and angle B = 24°. What is angle C (in degrees)?
  26. 26.In triangle ABC, angle A = 73° and angle B = 36°. What is angle C (in degrees)?
  27. 27.Can a triangle have sides of 5 cm, 4 cm and 6 cm? (a) No (b) Yes
  28. 28.In triangle ABC, angle A = 68° and angle B = 20°. What is angle C (in degrees)?
  29. 29.The angles of a triangle are in the ratio 3 : 5 : 7. What is the smallest angle (in degrees)?
  30. 30.The two interior opposite angles of a triangle are 61° and 60°. What is the exterior angle (in degrees)?
  31. 31.In an isosceles triangle, the two equal angles are 77° each. What is the third angle (in degrees)?
  32. 32.Can a triangle have sides of 9 cm, 16 cm and 11 cm? (a) Yes (b) No
  33. 33.Can a triangle have sides of 7 cm, 16 cm and 6 cm? (a) No (b) Yes
  34. 34.The angles of a triangle are in the ratio 3 : 4 : 5. What is the biggest angle (in degrees)?
  35. 35.The angles of a triangle are in the ratio 1 : 2 : 2. What is the biggest angle (in degrees)?
  36. 36.The two interior opposite angles of a triangle are 53° and 74°. What is the exterior angle (in degrees)?
  37. 37.In a right-angled triangle, one of the other two angles is 44°. What is the third angle (in degrees)?
  38. 38.An exterior angle of a triangle is 57°. One of its two interior opposite angles is 36°. What is the other one (in degrees)?
  39. 39.In triangle ABC, angle A = 93° and angle B = 61°. What is angle C (in degrees)?
  40. 40.An exterior angle of a triangle is 85°. One of its two interior opposite angles is 34°. What is the other one (in degrees)?

Answer key

  1. 73
  2. 34
  3. 43
  4. 48
  5. 18
  6. 16
  7. 15
  8. 38
  9. 107
  10. No
  11. 66
  12. 65
  13. 55
  14. 7
  15. No
  16. 84
  17. 49
  18. 107
  19. 103
  20. 18
  21. 34
  22. 36
  23. 24
  24. No
  25. 66
  26. 71
  27. Yes
  28. 92
  29. 36
  30. 121
  31. 26
  32. Yes
  33. No
  34. 75
  35. 72
  36. 127
  37. 46
  38. 21
  39. 26
  40. 51

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