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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 12 · 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 an isosceles triangle, the angle between the two equal sides is 138°. What is each of the other two angles (in degrees)?
  2. 2.In an isosceles triangle, the two equal angles are 81° each. What is the third angle (in degrees)?
  3. 3.The two interior opposite angles of a triangle are 74° and 45°. What is the exterior angle (in degrees)?
  4. 4.In an isosceles triangle, the angle between the two equal sides is 126°. What is each of the other two angles (in degrees)?
  5. 5.In an isosceles triangle, the angle between the two equal sides is 58°. What is each of the other two angles (in degrees)?
  6. 6.In triangle ABC, angle A = 66° and angle B = 46°. What is angle C (in degrees)?
  7. 7.In an isosceles triangle, the angle between the two equal sides is 122°. What is each of the other two angles (in degrees)?
  8. 8.In triangle ABC, angle A = 26° and angle B = 125°. What is angle C (in degrees)?
  9. 9.In an isosceles triangle, the angle between the two equal sides is 158°. What is each of the other two angles (in degrees)?
  10. 10.In triangle ABC, angle A = 82° and angle B = 67°. What is angle C (in degrees)?
  11. 11.Can a triangle have sides of 26 cm, 9 cm and 12 cm? (a) No (b) Yes
  12. 12.In triangle ABC, angle A = 38° and angle B = 69°. What is angle C (in degrees)?
  13. 13.In triangle ABC, angle A = 79° and angle B = 54°. What is angle C (in degrees)?
  14. 14.In a right-angled triangle, one of the other two angles is 62°. What is the third angle (in degrees)?
  15. 15.In an isosceles triangle, the angle between the two equal sides is 148°. What is each of the other two angles (in degrees)?
  16. 16.In a right-angled triangle, one of the other two angles is 58°. What is the third angle (in degrees)?
  17. 17.An exterior angle of a triangle is 116°. One of its two interior opposite angles is 74°. What is the other one (in degrees)?
  18. 18.The angles of a triangle are in the ratio 1 : 4 : 5. What is the smallest angle (in degrees)?
  19. 19.The angles of a triangle are in the ratio 2 : 2 : 5. What is the biggest angle (in degrees)?
  20. 20.An exterior angle of a triangle is 107°. One of its two interior opposite angles is 57°. What is the other one (in degrees)?
  21. 21.The angles of a triangle are in the ratio 2 : 3 : 5. What is the smallest angle (in degrees)?
  22. 22.The angles of a triangle are in the ratio 1 : 2 : 6. What is the biggest angle (in degrees)?
  23. 23.In a right-angled triangle, one of the other two angles is 41°. What is the third angle (in degrees)?
  24. 24.Can a triangle have sides of 12 cm, 2 cm and 15 cm? (a) No (b) Yes
  25. 25.In a right-angled triangle, one of the other two angles is 32°. What is the third angle (in degrees)?
  26. 26.In an isosceles triangle, the two equal angles are 22° each. What is the third angle (in degrees)?
  27. 27.The two interior opposite angles of a triangle are 53° and 48°. What is the exterior angle (in degrees)?
  28. 28.In triangle ABC, angle A = 39° and angle B = 73°. What is angle C (in degrees)?
  29. 29.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)?
  30. 30.The angles of a triangle are in the ratio 3 : 4 : 5. What is the biggest angle (in degrees)?
  31. 31.An exterior angle of a triangle is 95°. One of its two interior opposite angles is 32°. What is the other one (in degrees)?
  32. 32.Can a triangle have sides of 9 cm, 3 cm and 9 cm? (a) Yes (b) No
  33. 33.The angles of a triangle are in the ratio 2 : 3 : 4. What is the smallest angle (in degrees)?
  34. 34.In triangle ABC, angle A = 41° and angle B = 20°. What is angle C (in degrees)?
  35. 35.The two interior opposite angles of a triangle are 44° and 70°. What is the exterior angle (in degrees)?
  36. 36.In triangle ABC, angle A = 24° and angle B = 23°. What is angle C (in degrees)?
  37. 37.In a right-angled triangle, one of the other two angles is 11°. What is the third angle (in degrees)?
  38. 38.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)?
  39. 39.An exterior angle of a triangle is 104°. One of its two interior opposite angles is 29°. What is the other one (in degrees)?
  40. 40.In an isosceles triangle, the angle between the two equal sides is 74°. What is each of the other two angles (in degrees)?

Answer key

  1. 21
  2. 18
  3. 119
  4. 27
  5. 61
  6. 68
  7. 29
  8. 29
  9. 11
  10. 31
  11. No
  12. 73
  13. 47
  14. 28
  15. 16
  16. 32
  17. 42
  18. 18
  19. 100
  20. 50
  21. 36
  22. 120
  23. 49
  24. No
  25. 58
  26. 136
  27. 101
  28. 68
  29. 7
  30. 75
  31. 63
  32. Yes
  33. 40
  34. 119
  35. 114
  36. 133
  37. 79
  38. 24
  39. 75
  40. 53

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