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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 966 · 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 7 cm, 8 cm and 19 cm? (a) Yes (b) No
  2. 2.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)?
  3. 3.In an isosceles triangle, the angle between the two equal sides is 116°. What is each of the other two angles (in degrees)?
  4. 4.In a right-angled triangle, one of the other two angles is 27°. What is the third angle (in degrees)?
  5. 5.In triangle ABC, angle A = 65° and angle B = 64°. What is angle C (in degrees)?
  6. 6.The angles of a triangle are in the ratio 3 : 4 : 5. What is the smallest angle (in degrees)?
  7. 7.In triangle ABC, angle A = 61° and angle B = 55°. What is angle C (in degrees)?
  8. 8.The longest side of a right-angled triangle is 20 cm and one of the other sides is 16 cm. How long is the third side (in cm)?
  9. 9.The angles of a triangle are in the ratio 1 : 3 : 5. What is the biggest angle (in degrees)?
  10. 10.The two interior opposite angles of a triangle are 23° and 54°. What is the exterior angle (in degrees)?
  11. 11.In triangle ABC, angle A = 98° and angle B = 25°. What is angle C (in degrees)?
  12. 12.In triangle ABC, angle A = 45° and angle B = 42°. What is angle C (in degrees)?
  13. 13.The angles of a triangle are in the ratio 1 : 1 : 2. What is the biggest angle (in degrees)?
  14. 14.In an isosceles triangle, the angle between the two equal sides is 26°. What is each of the other two angles (in degrees)?
  15. 15.In a right-angled triangle, one of the other two angles is 54°. What is the third angle (in degrees)?
  16. 16.The two interior opposite angles of a triangle are 68° and 55°. What is the exterior angle (in degrees)?
  17. 17.In triangle ABC, angle A = 72° and angle B = 25°. What is angle C (in degrees)?
  18. 18.The angles of a triangle are in the ratio 2 : 3 : 5. What is the biggest angle (in degrees)?
  19. 19.The two interior opposite angles of a triangle are 63° and 59°. What is the exterior angle (in degrees)?
  20. 20.In a right-angled triangle, one of the other two angles is 58°. What is the third angle (in degrees)?
  21. 21.The two shorter sides of a right-angled triangle are 15 cm and 8 cm. How long is the longest side (in cm)?
  22. 22.In triangle ABC, angle A = 71° and angle B = 31°. What is angle C (in degrees)?
  23. 23.The two shorter sides of a right-angled triangle are 15 cm and 36 cm. How long is the longest side (in cm)?
  24. 24.The angles of a triangle are in the ratio 4 : 5 : 6. What is the biggest angle (in degrees)?
  25. 25.Can a triangle have sides of 8 cm, 8 cm and 9 cm? (a) Yes (b) No
  26. 26.In triangle ABC, angle A = 34° and angle B = 26°. What is angle C (in degrees)?
  27. 27.The two interior opposite angles of a triangle are 78° and 23°. What is the exterior angle (in degrees)?
  28. 28.In triangle ABC, angle A = 60° and angle B = 39°. What is angle C (in degrees)?
  29. 29.An exterior angle of a triangle is 69°. One of its two interior opposite angles is 29°. What is the other one (in degrees)?
  30. 30.An exterior angle of a triangle is 99°. One of its two interior opposite angles is 27°. What is the other one (in degrees)?
  31. 31.In a right-angled triangle, one of the other two angles is 68°. What is the third angle (in degrees)?
  32. 32.In a right-angled triangle, one of the other two angles is 21°. What is the third angle (in degrees)?
  33. 33.The angles of a triangle are in the ratio 1 : 3 : 5. What is the smallest angle (in degrees)?
  34. 34.In an isosceles triangle, the two equal angles are 79° each. What is the third angle (in degrees)?
  35. 35.Can a triangle have sides of 9 cm, 9 cm and 17 cm? (a) No (b) Yes
  36. 36.In triangle ABC, angle A = 52° and angle B = 80°. What is angle C (in degrees)?
  37. 37.The two interior opposite angles of a triangle are 34° and 36°. What is the exterior angle (in degrees)?
  38. 38.Can a triangle have sides of 9 cm, 5 cm and 18 cm? (a) Yes (b) No
  39. 39.The angles of a triangle are in the ratio 1 : 1 : 2. What is the smallest angle (in degrees)?
  40. 40.In an isosceles triangle, the two equal angles are 20° each. What is the third angle (in degrees)?

Answer key

  1. No
  2. 20
  3. 32
  4. 63
  5. 51
  6. 45
  7. 64
  8. 12
  9. 100
  10. 77
  11. 57
  12. 93
  13. 90
  14. 77
  15. 36
  16. 123
  17. 83
  18. 90
  19. 122
  20. 32
  21. 17
  22. 78
  23. 39
  24. 72
  25. Yes
  26. 120
  27. 101
  28. 81
  29. 40
  30. 72
  31. 22
  32. 69
  33. 20
  34. 22
  35. Yes
  36. 48
  37. 70
  38. No
  39. 45
  40. 140

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