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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 481 · 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.Can a triangle have sides of 23 cm, 10 cm and 12 cm? (a) Yes (b) No
  2. 2.In triangle ABC, angle A = 80° and angle B = 28°. What is angle C (in degrees)?
  3. 3.The angles of a triangle are in the ratio 5 : 6 : 7. What is the biggest angle (in degrees)?
  4. 4.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)?
  5. 5.In an isosceles triangle, the angle between the two equal sides is 82°. What is each of the other two angles (in degrees)?
  6. 6.An exterior angle of a triangle is 146°. One of its two interior opposite angles is 66°. What is the other one (in degrees)?
  7. 7.The angles of a triangle are in the ratio 2 : 3 : 5. What is the biggest angle (in degrees)?
  8. 8.In triangle ABC, angle A = 79° and angle B = 56°. What is angle C (in degrees)?
  9. 9.The angles of a triangle are in the ratio 1 : 3 : 5. What is the smallest angle (in degrees)?
  10. 10.In an isosceles triangle, the angle between the two equal sides is 28°. What is each of the other two angles (in degrees)?
  11. 11.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)?
  12. 12.In triangle ABC, angle A = 62° and angle B = 49°. What is angle C (in degrees)?
  13. 13.The two shorter sides of a right-angled triangle are 15 cm and 36 cm. How long is the longest side (in cm)?
  14. 14.In an isosceles triangle, the angle between the two equal sides is 122°. What is each of the other two angles (in degrees)?
  15. 15.Can a triangle have sides of 12 cm, 8 cm and 9 cm? (a) Yes (b) No
  16. 16.The angles of a triangle are in the ratio 3 : 3 : 4. What is the smallest angle (in degrees)?
  17. 17.An exterior angle of a triangle is 105°. One of its two interior opposite angles is 71°. What is the other one (in degrees)?
  18. 18.Can a triangle have sides of 7 cm, 4 cm and 9 cm? (a) Yes (b) No
  19. 19.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)?
  20. 20.The angles of a triangle are in the ratio 1 : 2 : 3. What is the biggest angle (in degrees)?
  21. 21.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)?
  22. 22.An exterior angle of a triangle is 138°. One of its two interior opposite angles is 71°. What is the other one (in degrees)?
  23. 23.The two shorter sides of a right-angled triangle are 15 cm and 8 cm. How long is the longest side (in cm)?
  24. 24.In a right-angled triangle, one of the other two angles is 35°. What is the third angle (in degrees)?
  25. 25.In triangle ABC, angle A = 86° and angle B = 32°. What is angle C (in degrees)?
  26. 26.In a right-angled triangle, one of the other two angles is 65°. What is the third angle (in degrees)?
  27. 27.The two shorter sides of a right-angled triangle are 24 cm and 7 cm. How long is the longest side (in cm)?
  28. 28.The two interior opposite angles of a triangle are 41° and 24°. What is the exterior angle (in degrees)?
  29. 29.In an isosceles triangle, the two equal angles are 51° each. What is the third angle (in degrees)?
  30. 30.In triangle ABC, angle A = 82° and angle B = 46°. What is angle C (in degrees)?
  31. 31.In a right-angled triangle, one of the other two angles is 32°. What is the third angle (in degrees)?
  32. 32.Can a triangle have sides of 6 cm, 8 cm and 15 cm? (a) Yes (b) No
  33. 33.In a right-angled triangle, one of the other two angles is 26°. What is the third angle (in degrees)?
  34. 34.In triangle ABC, angle A = 40° and angle B = 34°. What is angle C (in degrees)?
  35. 35.In an isosceles triangle, the two equal angles are 44° each. What is the third angle (in degrees)?
  36. 36.In triangle ABC, angle A = 27° and angle B = 35°. What is angle C (in degrees)?
  37. 37.In an isosceles triangle, the angle between the two equal sides is 102°. What is each of the other two angles (in degrees)?
  38. 38.In an isosceles triangle, the two equal angles are 69° each. What is the third angle (in degrees)?
  39. 39.In an isosceles triangle, the two equal angles are 26° each. What is the third angle (in degrees)?
  40. 40.An exterior angle of a triangle is 119°. One of its two interior opposite angles is 57°. What is the other one (in degrees)?

Answer key

  1. No
  2. 72
  3. 70
  4. 16
  5. 49
  6. 80
  7. 90
  8. 45
  9. 20
  10. 76
  11. 5
  12. 69
  13. 39
  14. 29
  15. Yes
  16. 54
  17. 34
  18. Yes
  19. 15
  20. 90
  21. 7
  22. 67
  23. 17
  24. 55
  25. 62
  26. 25
  27. 25
  28. 65
  29. 78
  30. 52
  31. 58
  32. No
  33. 64
  34. 106
  35. 92
  36. 118
  37. 39
  38. 42
  39. 128
  40. 62

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