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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 994 · 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 = 41° and angle B = 74°. What is angle C (in degrees)?
  2. 2.In an isosceles triangle, the two equal angles are 26° each. What is the third angle (in degrees)?
  3. 3.In triangle ABC, angle A = 54° and angle B = 77°. What is angle C (in degrees)?
  4. 4.The longest side of a right-angled triangle is 10 cm and one of the other sides is 6 cm. How long is the third side (in cm)?
  5. 5.In a right-angled triangle, one of the other two angles is 22°. What is the third angle (in degrees)?
  6. 6.The angles of a triangle are in the ratio 4 : 5 : 6. What is the biggest angle (in degrees)?
  7. 7.In triangle ABC, angle A = 66° and angle B = 93°. What is angle C (in degrees)?
  8. 8.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)?
  9. 9.The two interior opposite angles of a triangle are 49° and 34°. What is the exterior angle (in degrees)?
  10. 10.The angles of a triangle are in the ratio 1 : 2 : 2. What is the biggest angle (in degrees)?
  11. 11.In a right-angled triangle, one of the other two angles is 18°. What is the third angle (in degrees)?
  12. 12.In a right-angled triangle, one of the other two angles is 21°. What is the third angle (in degrees)?
  13. 13.The longest side of a right-angled triangle is 15 cm and one of the other sides is 9 cm. How long is the third side (in cm)?
  14. 14.In triangle ABC, angle A = 51° and angle B = 33°. What is angle C (in degrees)?
  15. 15.In a right-angled triangle, one of the other two angles is 39°. What is the third angle (in degrees)?
  16. 16.In an isosceles triangle, the two equal angles are 73° each. What is the third angle (in degrees)?
  17. 17.The angles of a triangle are in the ratio 3 : 3 : 4. What is the biggest angle (in degrees)?
  18. 18.In triangle ABC, angle A = 25° and angle B = 68°. What is angle C (in degrees)?
  19. 19.An exterior angle of a triangle is 71°. One of its two interior opposite angles is 20°. What is the other one (in degrees)?
  20. 20.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)?
  21. 21.Can a triangle have sides of 7 cm, 15 cm and 6 cm? (a) Yes (b) No
  22. 22.The angles of a triangle are in the ratio 5 : 6 : 7. What is the smallest angle (in degrees)?
  23. 23.An exterior angle of a triangle is 115°. One of its two interior opposite angles is 66°. What is the other one (in degrees)?
  24. 24.The angles of a triangle are in the ratio 2 : 2 : 5. What is the smallest angle (in degrees)?
  25. 25.The angles of a triangle are in the ratio 1 : 2 : 3. What is the smallest angle (in degrees)?
  26. 26.In an isosceles triangle, the two equal angles are 52° each. What is the third angle (in degrees)?
  27. 27.In an isosceles triangle, the two equal angles are 24° each. What is the third angle (in degrees)?
  28. 28.The two shorter sides of a right-angled triangle are 15 cm and 8 cm. How long is the longest side (in cm)?
  29. 29.In an isosceles triangle, the angle between the two equal sides is 120°. What is each of the other two angles (in degrees)?
  30. 30.In an isosceles triangle, the angle between the two equal sides is 58°. What is each of the other two angles (in degrees)?
  31. 31.In an isosceles triangle, the two equal angles are 53° each. What is the third angle (in degrees)?
  32. 32.In an isosceles triangle, the angle between the two equal sides is 40°. What is each of the other two angles (in degrees)?
  33. 33.The angles of a triangle are in the ratio 1 : 1 : 2. What is the biggest angle (in degrees)?
  34. 34.Can a triangle have sides of 13 cm, 8 cm and 5 cm? (a) No (b) Yes
  35. 35.In triangle ABC, angle A = 23° and angle B = 124°. What is angle C (in degrees)?
  36. 36.The angles of a triangle are in the ratio 1 : 3 : 5. What is the biggest angle (in degrees)?
  37. 37.The angles of a triangle are in the ratio 2 : 7 : 9. What is the biggest angle (in degrees)?
  38. 38.An exterior angle of a triangle is 118°. One of its two interior opposite angles is 68°. What is the other one (in degrees)?
  39. 39.An exterior angle of a triangle is 123°. One of its two interior opposite angles is 51°. What is the other one (in degrees)?
  40. 40.In a right-angled triangle, one of the other two angles is 44°. What is the third angle (in degrees)?

Answer key

  1. 65
  2. 128
  3. 49
  4. 8
  5. 68
  6. 72
  7. 21
  8. 15
  9. 83
  10. 72
  11. 72
  12. 69
  13. 12
  14. 96
  15. 51
  16. 34
  17. 72
  18. 87
  19. 51
  20. 15
  21. No
  22. 50
  23. 49
  24. 40
  25. 30
  26. 76
  27. 132
  28. 17
  29. 30
  30. 61
  31. 74
  32. 70
  33. 90
  34. No
  35. 33
  36. 100
  37. 90
  38. 50
  39. 72
  40. 46

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