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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 229 · 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 = 67° and angle B = 71°. What is angle C (in degrees)?
  2. 2.In an isosceles triangle, the two equal angles are 65° each. What is the third angle (in degrees)?
  3. 3.In an isosceles triangle, the angle between the two equal sides is 140°. What is each of the other two angles (in degrees)?
  4. 4.In a right-angled triangle, one of the other two angles is 68°. What is the third angle (in degrees)?
  5. 5.An exterior angle of a triangle is 86°. One of its two interior opposite angles is 26°. What is the other one (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 = 58° and angle B = 83°. What is angle C (in degrees)?
  8. 8.The longest side of a right-angled triangle is 25 cm and one of the other sides is 7 cm. How long is the third side (in cm)?
  9. 9.In triangle ABC, angle A = 85° and angle B = 26°. What is angle C (in degrees)?
  10. 10.In a right-angled triangle, one of the other two angles is 50°. What is the third angle (in degrees)?
  11. 11.In triangle ABC, angle A = 55° and angle B = 23°. What is angle C (in degrees)?
  12. 12.The two interior opposite angles of a triangle are 20° and 74°. What is the exterior angle (in degrees)?
  13. 13.In an isosceles triangle, the two equal angles are 81° each. What is the third angle (in degrees)?
  14. 14.In triangle ABC, angle A = 73° and angle B = 32°. What is angle C (in degrees)?
  15. 15.In an isosceles triangle, the angle between the two equal sides is 68°. What is each of the other two angles (in degrees)?
  16. 16.The longest side of a right-angled triangle is 5 cm and one of the other sides is 4 cm. How long is the third side (in cm)?
  17. 17.The longest side of a right-angled triangle is 5 cm and one of the other sides is 3 cm. How long is the third side (in cm)?
  18. 18.In an isosceles triangle, the angle between the two equal sides is 88°. What is each of the other two angles (in degrees)?
  19. 19.An exterior angle of a triangle is 86°. One of its two interior opposite angles is 41°. What is the other one (in degrees)?
  20. 20.The angles of a triangle are in the ratio 3 : 5 : 7. What is the smallest angle (in degrees)?
  21. 21.Can a triangle have sides of 7 cm, 8 cm and 2 cm? (a) No (b) Yes
  22. 22.The two shorter sides of a right-angled triangle are 36 cm and 15 cm. How long is the longest side (in cm)?
  23. 23.The angles of a triangle are in the ratio 2 : 3 : 5. What is the smallest angle (in degrees)?
  24. 24.In an isosceles triangle, the angle between the two equal sides is 120°. What is each of the other two angles (in degrees)?
  25. 25.In an isosceles triangle, the angle between the two equal sides is 142°. What is each of the other two angles (in degrees)?
  26. 26.The two interior opposite angles of a triangle are 26° and 42°. What is the exterior angle (in degrees)?
  27. 27.The angles of a triangle are in the ratio 3 : 5 : 7. What is the biggest angle (in degrees)?
  28. 28.The two shorter sides of a right-angled triangle are 3 cm and 4 cm. How long is the longest side (in cm)?
  29. 29.The two shorter sides of a right-angled triangle are 20 cm and 15 cm. How long is the longest side (in cm)?
  30. 30.In a right-angled triangle, one of the other two angles is 65°. What is the third angle (in degrees)?
  31. 31.The angles of a triangle are in the ratio 2 : 2 : 5. What is the smallest angle (in degrees)?
  32. 32.In a right-angled triangle, one of the other two angles is 11°. What is the third angle (in degrees)?
  33. 33.In triangle ABC, angle A = 64° and angle B = 45°. What is angle C (in degrees)?
  34. 34.In an isosceles triangle, the two equal angles are 75° each. What is the third angle (in degrees)?
  35. 35.The two shorter sides of a right-angled triangle are 7 cm and 24 cm. How long is the longest side (in cm)?
  36. 36.An exterior angle of a triangle is 95°. One of its two interior opposite angles is 48°. What is the other one (in degrees)?
  37. 37.In triangle ABC, angle A = 91° and angle B = 38°. What is angle C (in degrees)?
  38. 38.The angles of a triangle are in the ratio 1 : 2 : 6. What is the smallest angle (in degrees)?
  39. 39.In triangle ABC, angle A = 20° and angle B = 70°. What is angle C (in degrees)?
  40. 40.In an isosceles triangle, the two equal angles are 46° each. What is the third angle (in degrees)?

Answer key

  1. 42
  2. 50
  3. 20
  4. 22
  5. 60
  6. 45
  7. 39
  8. 24
  9. 69
  10. 40
  11. 102
  12. 94
  13. 18
  14. 75
  15. 56
  16. 3
  17. 4
  18. 46
  19. 45
  20. 36
  21. Yes
  22. 39
  23. 36
  24. 30
  25. 19
  26. 68
  27. 84
  28. 5
  29. 25
  30. 25
  31. 40
  32. 79
  33. 71
  34. 30
  35. 25
  36. 47
  37. 51
  38. 20
  39. 90
  40. 88

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