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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 734 · 40 sums
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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 an isosceles triangle, the angle between the two equal sides is 80°. What is each of the other two angles (in degrees)?
  2. 2.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)?
  3. 3.In a right-angled triangle, one of the other two angles is 21°. What is the third angle (in degrees)?
  4. 4.An exterior angle of a triangle is 116°. One of its two interior opposite angles is 46°. What is the other one (in degrees)?
  5. 5.Can a triangle have sides of 8 cm, 10 cm and 9 cm? (a) No (b) Yes
  6. 6.The angles of a triangle are in the ratio 3 : 5 : 7. What is the biggest angle (in degrees)?
  7. 7.An exterior angle of a triangle is 76°. One of its two interior opposite angles is 40°. What is the other one (in degrees)?
  8. 8.An exterior angle of a triangle is 114°. One of its two interior opposite angles is 67°. What is the other one (in degrees)?
  9. 9.Can a triangle have sides of 9 cm, 8 cm and 8 cm? (a) No (b) Yes
  10. 10.The longest side of a right-angled triangle is 10 cm and one of the other sides is 8 cm. How long is the third side (in cm)?
  11. 11.In triangle ABC, angle A = 24° and angle B = 22°. What is angle C (in degrees)?
  12. 12.In a right-angled triangle, one of the other two angles is 75°. What is the third angle (in degrees)?
  13. 13.In an isosceles triangle, the two equal angles are 65° each. What is the third angle (in degrees)?
  14. 14.In a right-angled triangle, one of the other two angles is 54°. What is the third angle (in degrees)?
  15. 15.In an isosceles triangle, the angle between the two equal sides is 128°. What is each of the other two angles (in degrees)?
  16. 16.The angles of a triangle are in the ratio 2 : 3 : 4. What is the smallest angle (in degrees)?
  17. 17.The angles of a triangle are in the ratio 3 : 4 : 5. What is the smallest angle (in degrees)?
  18. 18.Can a triangle have sides of 5 cm, 3 cm and 11 cm? (a) No (b) Yes
  19. 19.An exterior angle of a triangle is 60°. One of its two interior opposite angles is 25°. What is the other one (in degrees)?
  20. 20.In a right-angled triangle, one of the other two angles is 79°. What is the third angle (in degrees)?
  21. 21.In an isosceles triangle, the angle between the two equal sides is 146°. What is each of the other two angles (in degrees)?
  22. 22.The angles of a triangle are in the ratio 2 : 2 : 5. What is the smallest angle (in degrees)?
  23. 23.In triangle ABC, angle A = 77° and angle B = 60°. What is angle C (in degrees)?
  24. 24.An exterior angle of a triangle is 120°. One of its two interior opposite angles is 45°. What is the other one (in degrees)?
  25. 25.The angles of a triangle are in the ratio 2 : 3 : 5. What is the smallest angle (in degrees)?
  26. 26.The two interior opposite angles of a triangle are 77° and 44°. What is the exterior angle (in degrees)?
  27. 27.In triangle ABC, angle A = 94° and angle B = 58°. What is angle C (in degrees)?
  28. 28.In an isosceles triangle, the angle between the two equal sides is 144°. What is each of the other two angles (in degrees)?
  29. 29.The longest side of a right-angled triangle is 20 cm and one of the other sides is 16 cm. How long is the third side (in cm)?
  30. 30.The angles of a triangle are in the ratio 2 : 7 : 9. What is the biggest angle (in degrees)?
  31. 31.An exterior angle of a triangle is 80°. One of its two interior opposite angles is 30°. What is the other one (in degrees)?
  32. 32.In triangle ABC, angle A = 54° and angle B = 46°. What is angle C (in degrees)?
  33. 33.The two interior opposite angles of a triangle are 77° and 63°. What is the exterior angle (in degrees)?
  34. 34.The angles of a triangle are in the ratio 1 : 3 : 5. What is the smallest angle (in degrees)?
  35. 35.The two interior opposite angles of a triangle are 37° and 25°. What is the exterior angle (in degrees)?
  36. 36.In triangle ABC, angle A = 73° and angle B = 29°. What is angle C (in degrees)?
  37. 37.In triangle ABC, angle A = 32° and angle B = 39°. What is angle C (in degrees)?
  38. 38.Can a triangle have sides of 9 cm, 11 cm and 8 cm? (a) Yes (b) No
  39. 39.In an isosceles triangle, the angle between the two equal sides is 22°. What is each of the other two angles (in degrees)?
  40. 40.In triangle ABC, angle A = 22° and angle B = 87°. What is angle C (in degrees)?

Answer key

  1. 50
  2. 15
  3. 69
  4. 70
  5. Yes
  6. 84
  7. 36
  8. 47
  9. Yes
  10. 6
  11. 134
  12. 15
  13. 50
  14. 36
  15. 26
  16. 40
  17. 45
  18. No
  19. 35
  20. 11
  21. 17
  22. 40
  23. 43
  24. 75
  25. 36
  26. 121
  27. 28
  28. 18
  29. 12
  30. 90
  31. 50
  32. 80
  33. 140
  34. 20
  35. 62
  36. 78
  37. 109
  38. Yes
  39. 79
  40. 71

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