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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 772 · 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 triangle ABC, angle A = 55° and angle B = 100°. What is angle C (in degrees)?
  2. 2.The longest side of a right-angled triangle is 39 cm and one of the other sides is 15 cm. How long is the third side (in cm)?
  3. 3.In triangle ABC, angle A = 22° and angle B = 23°. What is angle C (in degrees)?
  4. 4.The two interior opposite angles of a triangle are 80° and 55°. What is the exterior angle (in degrees)?
  5. 5.The angles of a triangle are in the ratio 2 : 3 : 4. What is the biggest angle (in degrees)?
  6. 6.The angles of a triangle are in the ratio 4 : 5 : 6. What is the smallest angle (in degrees)?
  7. 7.The two interior opposite angles of a triangle are 59° and 76°. What is the exterior angle (in degrees)?
  8. 8.In an isosceles triangle, the two equal angles are 36° each. What is the third angle (in degrees)?
  9. 9.The angles of a triangle are in the ratio 3 : 5 : 7. What is the biggest angle (in degrees)?
  10. 10.In a right-angled triangle, one of the other two angles is 14°. What is the third angle (in degrees)?
  11. 11.In an isosceles triangle, the angle between the two equal sides is 116°. What is each of the other two angles (in degrees)?
  12. 12.In triangle ABC, angle A = 49° and angle B = 30°. What is angle C (in degrees)?
  13. 13.Can a triangle have sides of 6 cm, 6 cm and 7 cm? (a) No (b) Yes
  14. 14.In a right-angled triangle, one of the other two angles is 11°. What is the third angle (in degrees)?
  15. 15.In a right-angled triangle, one of the other two angles is 31°. What is the third angle (in degrees)?
  16. 16.In a right-angled triangle, one of the other two angles is 38°. What is the third angle (in degrees)?
  17. 17.The two interior opposite angles of a triangle are 39° and 37°. What is the exterior angle (in degrees)?
  18. 18.The two shorter sides of a right-angled triangle are 24 cm and 7 cm. How long is the longest side (in cm)?
  19. 19.In an isosceles triangle, the angle between the two equal sides is 60°. What is each of the other two angles (in degrees)?
  20. 20.Can a triangle have sides of 2 cm, 11 cm and 5 cm? (a) Yes (b) No
  21. 21.In an isosceles triangle, the two equal angles are 43° each. What is the third angle (in degrees)?
  22. 22.The two interior opposite angles of a triangle are 47° and 41°. What is the exterior angle (in degrees)?
  23. 23.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)?
  24. 24.The two interior opposite angles of a triangle are 56° and 26°. What is the exterior angle (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.In an isosceles triangle, the angle between the two equal sides is 126°. What is each of the other two angles (in degrees)?
  27. 27.In triangle ABC, angle A = 71° and angle B = 87°. What is angle C (in degrees)?
  28. 28.Can a triangle have sides of 10 cm, 4 cm and 15 cm? (a) Yes (b) No
  29. 29.In a right-angled triangle, one of the other two angles is 57°. What is the third angle (in degrees)?
  30. 30.In an isosceles triangle, the angle between the two equal sides is 26°. What is each of the other two angles (in degrees)?
  31. 31.In a right-angled triangle, one of the other two angles is 39°. What is the third angle (in degrees)?
  32. 32.Can a triangle have sides of 10 cm, 26 cm and 11 cm? (a) Yes (b) No
  33. 33.The two interior opposite angles of a triangle are 54° and 41°. What is the exterior angle (in degrees)?
  34. 34.In a right-angled triangle, one of the other two angles is 61°. What is the third angle (in degrees)?
  35. 35.An exterior angle of a triangle is 119°. One of its two interior opposite angles is 77°. What is the other one (in degrees)?
  36. 36.The two shorter sides of a right-angled triangle are 7 cm and 24 cm. How long is the longest side (in cm)?
  37. 37.The angles of a triangle are in the ratio 5 : 6 : 7. What is the smallest angle (in degrees)?
  38. 38.In an isosceles triangle, the angle between the two equal sides is 86°. What is each of the other two angles (in degrees)?
  39. 39.Can a triangle have sides of 10 cm, 2 cm and 9 cm? (a) No (b) Yes
  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. 25
  2. 36
  3. 135
  4. 135
  5. 80
  6. 48
  7. 135
  8. 108
  9. 84
  10. 76
  11. 32
  12. 101
  13. Yes
  14. 79
  15. 59
  16. 52
  17. 76
  18. 25
  19. 60
  20. No
  21. 94
  22. 88
  23. 10
  24. 82
  25. 36
  26. 27
  27. 22
  28. No
  29. 33
  30. 77
  31. 51
  32. No
  33. 95
  34. 29
  35. 42
  36. 25
  37. 50
  38. 47
  39. Yes
  40. 5

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