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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 834 · 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 a right-angled triangle, one of the other two angles is 61°. What is the third angle (in degrees)?
  2. 2.The longest side of a right-angled triangle is 15 cm and one of the other sides is 9 cm. How long is the third side (in cm)?
  3. 3.In an isosceles triangle, the two equal angles are 61° each. What is the third angle (in degrees)?
  4. 4.The two interior opposite angles of a triangle are 30° and 46°. What is the exterior angle (in degrees)?
  5. 5.In a right-angled triangle, one of the other two angles is 70°. What is the third angle (in degrees)?
  6. 6.In an isosceles triangle, the two equal angles are 83° each. What is the third angle (in degrees)?
  7. 7.The angles of a triangle are in the ratio 1 : 2 : 3. What is the biggest angle (in degrees)?
  8. 8.In an isosceles triangle, the angle between the two equal sides is 98°. What is each of the other two angles (in degrees)?
  9. 9.In an isosceles triangle, the angle between the two equal sides is 58°. What is each of the other two angles (in degrees)?
  10. 10.In a right-angled triangle, one of the other two angles is 12°. What is the third angle (in degrees)?
  11. 11.In a right-angled triangle, one of the other two angles is 32°. What is the third angle (in degrees)?
  12. 12.The angles of a triangle are in the ratio 2 : 2 : 5. What is the biggest angle (in degrees)?
  13. 13.An exterior angle of a triangle is 126°. One of its two interior opposite angles is 78°. What is the other one (in degrees)?
  14. 14.The angles of a triangle are in the ratio 3 : 3 : 4. What is the smallest angle (in degrees)?
  15. 15.The two interior opposite angles of a triangle are 62° and 49°. What is the exterior angle (in degrees)?
  16. 16.In triangle ABC, angle A = 78° and angle B = 25°. What is angle C (in degrees)?
  17. 17.Can a triangle have sides of 22 cm, 11 cm and 9 cm? (a) Yes (b) No
  18. 18.In a right-angled triangle, one of the other two angles is 69°. What is the third angle (in degrees)?
  19. 19.An exterior angle of a triangle is 75°. One of its two interior opposite angles is 44°. What is the other one (in degrees)?
  20. 20.In an isosceles triangle, the angle between the two equal sides is 128°. What is each of the other two angles (in degrees)?
  21. 21.An exterior angle of a triangle is 109°. One of its two interior opposite angles is 80°. What is the other one (in degrees)?
  22. 22.In triangle ABC, angle A = 62° and angle B = 42°. What is angle C (in degrees)?
  23. 23.In an isosceles triangle, the two equal angles are 66° each. What is the third angle (in degrees)?
  24. 24.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)?
  25. 25.In triangle ABC, angle A = 81° and angle B = 58°. What is angle C (in degrees)?
  26. 26.In an isosceles triangle, the angle between the two equal sides is 152°. What is each of the other two angles (in degrees)?
  27. 27.Can a triangle have sides of 3 cm, 8 cm and 7 cm? (a) Yes (b) No
  28. 28.In a right-angled triangle, one of the other two angles is 19°. What is the third angle (in degrees)?
  29. 29.In triangle ABC, angle A = 51° and angle B = 30°. What is angle C (in degrees)?
  30. 30.In a right-angled triangle, one of the other two angles is 68°. What is the third angle (in degrees)?
  31. 31.In a right-angled triangle, one of the other two angles is 55°. What is the third angle (in degrees)?
  32. 32.In a right-angled triangle, one of the other two angles is 11°. What is the third angle (in degrees)?
  33. 33.Can a triangle have sides of 13 cm, 4 cm and 5 cm? (a) Yes (b) No
  34. 34.The two shorter sides of a right-angled triangle are 6 cm and 8 cm. How long is the longest side (in cm)?
  35. 35.In triangle ABC, angle A = 29° and angle B = 116°. What is angle C (in degrees)?
  36. 36.The longest side of a right-angled triangle is 17 cm and one of the other sides is 15 cm. How long is the third side (in cm)?
  37. 37.In triangle ABC, angle A = 39° and angle B = 55°. What is angle C (in degrees)?
  38. 38.In triangle ABC, angle A = 28° and angle B = 103°. What is angle C (in degrees)?
  39. 39.In an isosceles triangle, the angle between the two equal sides is 86°. What is each of the other two angles (in degrees)?
  40. 40.In an isosceles triangle, the angle between the two equal sides is 158°. What is each of the other two angles (in degrees)?

Answer key

  1. 29
  2. 12
  3. 58
  4. 76
  5. 20
  6. 14
  7. 90
  8. 41
  9. 61
  10. 78
  11. 58
  12. 100
  13. 48
  14. 54
  15. 111
  16. 77
  17. No
  18. 21
  19. 31
  20. 26
  21. 29
  22. 76
  23. 48
  24. 15
  25. 41
  26. 14
  27. Yes
  28. 71
  29. 99
  30. 22
  31. 35
  32. 79
  33. No
  34. 10
  35. 35
  36. 8
  37. 86
  38. 49
  39. 47
  40. 11

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