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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 748 · 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 56°. What is each of the other two angles (in degrees)?
  2. 2.In a right-angled triangle, one of the other two angles is 52°. What is the third angle (in degrees)?
  3. 3.In a right-angled triangle, one of the other two angles is 14°. What is the third angle (in degrees)?
  4. 4.Can a triangle have sides of 12 cm, 6 cm and 19 cm? (a) No (b) Yes
  5. 5.The two shorter sides of a right-angled triangle are 15 cm and 36 cm. How long is the longest side (in cm)?
  6. 6.In an isosceles triangle, the angle between the two equal sides is 92°. What is each of the other two angles (in degrees)?
  7. 7.In triangle ABC, angle A = 21° and angle B = 101°. What is angle C (in degrees)?
  8. 8.In triangle ABC, angle A = 37° and angle B = 82°. What is angle C (in degrees)?
  9. 9.In an isosceles triangle, the two equal angles are 80° each. What is the third angle (in degrees)?
  10. 10.In a right-angled triangle, one of the other two angles is 71°. What is the third angle (in degrees)?
  11. 11.In triangle ABC, angle A = 83° and angle B = 23°. What is angle C (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.In a right-angled triangle, one of the other two angles is 22°. What is the third angle (in degrees)?
  14. 14.In a right-angled triangle, one of the other two angles is 34°. What is the third angle (in degrees)?
  15. 15.In an isosceles triangle, the two equal angles are 44° each. What is the third angle (in degrees)?
  16. 16.Can a triangle have sides of 9 cm, 23 cm and 11 cm? (a) Yes (b) No
  17. 17.In a right-angled triangle, one of the other two angles is 40°. What is the third angle (in degrees)?
  18. 18.In triangle ABC, angle A = 93° and angle B = 29°. What is angle C (in degrees)?
  19. 19.The two interior opposite angles of a triangle are 74° and 54°. What is the exterior angle (in degrees)?
  20. 20.In a right-angled triangle, one of the other two angles is 25°. What is the third angle (in degrees)?
  21. 21.In a right-angled triangle, one of the other two angles is 13°. What is the third angle (in degrees)?
  22. 22.In triangle ABC, angle A = 75° and angle B = 76°. What is angle C (in degrees)?
  23. 23.Can a triangle have sides of 8 cm, 3 cm and 10 cm? (a) Yes (b) No
  24. 24.In triangle ABC, angle A = 80° and angle B = 76°. What is angle C (in degrees)?
  25. 25.In a right-angled triangle, one of the other two angles is 28°. What is the third angle (in degrees)?
  26. 26.In an isosceles triangle, the angle between the two equal sides is 94°. What is each of the other two angles (in degrees)?
  27. 27.The longest side of a right-angled triangle is 39 cm and one of the other sides is 36 cm. How long is the third side (in cm)?
  28. 28.An exterior angle of a triangle is 99°. One of its two interior opposite angles is 60°. What is the other one (in degrees)?
  29. 29.In a right-angled triangle, one of the other two angles is 69°. What is the third angle (in degrees)?
  30. 30.In an isosceles triangle, the angle between the two equal sides is 32°. What is each of the other two angles (in degrees)?
  31. 31.Can a triangle have sides of 7 cm, 5 cm and 12 cm? (a) No (b) Yes
  32. 32.In an isosceles triangle, the angle between the two equal sides is 82°. What is each of the other two angles (in degrees)?
  33. 33.The angles of a triangle are in the ratio 3 : 5 : 7. What is the smallest angle (in degrees)?
  34. 34.In an isosceles triangle, the angle between the two equal sides is 112°. What is each of the other two angles (in degrees)?
  35. 35.The angles of a triangle are in the ratio 1 : 4 : 5. What is the smallest angle (in degrees)?
  36. 36.An exterior angle of a triangle is 106°. One of its two interior opposite angles is 39°. What is the other one (in degrees)?
  37. 37.In an isosceles triangle, the two equal angles are 21° each. What is the third angle (in degrees)?
  38. 38.The longest side of a right-angled triangle is 26 cm and one of the other sides is 24 cm. How long is the third side (in cm)?
  39. 39.The angles of a triangle are in the ratio 1 : 3 : 5. What is the smallest angle (in degrees)?
  40. 40.The longest side of a right-angled triangle is 13 cm and one of the other sides is 12 cm. How long is the third side (in cm)?

Answer key

  1. 62
  2. 38
  3. 76
  4. No
  5. 39
  6. 44
  7. 58
  8. 61
  9. 20
  10. 19
  11. 74
  12. 100
  13. 68
  14. 56
  15. 92
  16. No
  17. 50
  18. 58
  19. 128
  20. 65
  21. 77
  22. 29
  23. Yes
  24. 24
  25. 62
  26. 43
  27. 15
  28. 39
  29. 21
  30. 74
  31. No
  32. 49
  33. 36
  34. 34
  35. 18
  36. 67
  37. 138
  38. 10
  39. 20
  40. 5

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