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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 217 · 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.The angles of a triangle are in the ratio 2 : 2 : 5. What is the biggest angle (in degrees)?
  2. 2.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)?
  3. 3.The angles of a triangle are in the ratio 1 : 1 : 2. What is the biggest angle (in degrees)?
  4. 4.In a right-angled triangle, one of the other two angles is 51°. What is the third angle (in degrees)?
  5. 5.The angles of a triangle are in the ratio 3 : 4 : 5. What is the smallest angle (in degrees)?
  6. 6.In a right-angled triangle, one of the other two angles is 42°. What is the third angle (in degrees)?
  7. 7.Can a triangle have sides of 2 cm, 9 cm and 16 cm? (a) Yes (b) No
  8. 8.An exterior angle of a triangle is 60°. One of its two interior opposite angles is 37°. What is the other one (in degrees)?
  9. 9.An exterior angle of a triangle is 95°. One of its two interior opposite angles is 45°. What is the other one (in degrees)?
  10. 10.In a right-angled triangle, one of the other two angles is 35°. What is the third angle (in degrees)?
  11. 11.Can a triangle have sides of 21 cm, 9 cm and 12 cm? (a) Yes (b) No
  12. 12.In triangle ABC, angle A = 73° and angle B = 33°. What is angle C (in degrees)?
  13. 13.In a right-angled triangle, one of the other two angles is 34°. What is the third angle (in degrees)?
  14. 14.In a right-angled triangle, one of the other two angles is 29°. What is the third angle (in degrees)?
  15. 15.In an isosceles triangle, the angle between the two equal sides is 102°. What is each of the other two angles (in degrees)?
  16. 16.In an isosceles triangle, the angle between the two equal sides is 132°. What is each of the other two angles (in degrees)?
  17. 17.Can a triangle have sides of 5 cm, 12 cm and 8 cm? (a) Yes (b) No
  18. 18.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)?
  19. 19.An exterior angle of a triangle is 112°. One of its two interior opposite angles is 80°. What is the other one (in degrees)?
  20. 20.The angles of a triangle are in the ratio 1 : 2 : 3. What is the smallest angle (in degrees)?
  21. 21.An exterior angle of a triangle is 107°. One of its two interior opposite angles is 54°. What is the other one (in degrees)?
  22. 22.Can a triangle have sides of 10 cm, 11 cm and 2 cm? (a) Yes (b) No
  23. 23.The two interior opposite angles of a triangle are 48° and 77°. What is the exterior angle (in degrees)?
  24. 24.In triangle ABC, angle A = 28° and angle B = 46°. What is angle C (in degrees)?
  25. 25.The angles of a triangle are in the ratio 3 : 5 : 7. What is the smallest angle (in degrees)?
  26. 26.Can a triangle have sides of 14 cm, 4 cm and 10 cm? (a) Yes (b) No
  27. 27.In an isosceles triangle, the two equal angles are 66° each. What is the third angle (in degrees)?
  28. 28.The longest side of a right-angled triangle is 25 cm and one of the other sides is 15 cm. How long is the third side (in cm)?
  29. 29.The angles of a triangle are in the ratio 2 : 7 : 9. What is the biggest angle (in degrees)?
  30. 30.The angles of a triangle are in the ratio 2 : 3 : 5. What is the biggest angle (in degrees)?
  31. 31.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)?
  32. 32.In an isosceles triangle, the angle between the two equal sides is 48°. What is each of the other two angles (in degrees)?
  33. 33.An exterior angle of a triangle is 131°. One of its two interior opposite angles is 62°. What is the other one (in degrees)?
  34. 34.In triangle ABC, angle A = 79° and angle B = 44°. What is angle C (in degrees)?
  35. 35.The two interior opposite angles of a triangle are 20° and 44°. What is the exterior angle (in degrees)?
  36. 36.In an isosceles triangle, the two equal angles are 73° each. What is the third angle (in degrees)?
  37. 37.The angles of a triangle are in the ratio 5 : 6 : 7. What is the smallest angle (in degrees)?
  38. 38.An exterior angle of a triangle is 106°. One of its two interior opposite angles is 31°. What is the other one (in degrees)?
  39. 39.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)?
  40. 40.The two interior opposite angles of a triangle are 42° and 71°. What is the exterior angle (in degrees)?

Answer key

  1. 100
  2. 5
  3. 90
  4. 39
  5. 45
  6. 48
  7. No
  8. 23
  9. 50
  10. 55
  11. No
  12. 74
  13. 56
  14. 61
  15. 39
  16. 24
  17. Yes
  18. 8
  19. 32
  20. 30
  21. 53
  22. Yes
  23. 125
  24. 106
  25. 36
  26. No
  27. 48
  28. 20
  29. 90
  30. 90
  31. 7
  32. 66
  33. 69
  34. 57
  35. 64
  36. 34
  37. 50
  38. 75
  39. 10
  40. 113

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