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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 618 · 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 a right-angled triangle, one of the other two angles is 70°. What is the third angle (in degrees)?
  2. 2.In triangle ABC, angle A = 27° and angle B = 48°. What is angle C (in degrees)?
  3. 3.In triangle ABC, angle A = 88° and angle B = 59°. What is angle C (in degrees)?
  4. 4.In an isosceles triangle, the angle between the two equal sides is 54°. What is each of the other two angles (in degrees)?
  5. 5.Can a triangle have sides of 22 cm, 7 cm and 12 cm? (a) No (b) Yes
  6. 6.In an isosceles triangle, the two equal angles are 50° each. What is the third angle (in degrees)?
  7. 7.The angles of a triangle are in the ratio 3 : 4 : 5. What is the biggest angle (in degrees)?
  8. 8.In triangle ABC, angle A = 67° and angle B = 49°. What is angle C (in degrees)?
  9. 9.In an isosceles triangle, the angle between the two equal sides is 138°. What is each of the other two angles (in degrees)?
  10. 10.The two shorter sides of a right-angled triangle are 15 cm and 36 cm. How long is the longest side (in cm)?
  11. 11.Can a triangle have sides of 4 cm, 9 cm and 4 cm? (a) Yes (b) No
  12. 12.An exterior angle of a triangle is 48°. One of its two interior opposite angles is 26°. What is the other one (in degrees)?
  13. 13.Can a triangle have sides of 8 cm, 20 cm and 9 cm? (a) Yes (b) No
  14. 14.The angles of a triangle are in the ratio 2 : 2 : 5. What is the biggest angle (in degrees)?
  15. 15.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)?
  16. 16.In a right-angled triangle, one of the other two angles is 14°. What is the third angle (in degrees)?
  17. 17.An exterior angle of a triangle is 95°. One of its two interior opposite angles is 36°. What is the other one (in degrees)?
  18. 18.Can a triangle have sides of 10 cm, 10 cm and 9 cm? (a) No (b) Yes
  19. 19.In a right-angled triangle, one of the other two angles is 59°. What is the third angle (in degrees)?
  20. 20.The angles of a triangle are in the ratio 1 : 3 : 5. What is the biggest angle (in degrees)?
  21. 21.The two interior opposite angles of a triangle are 61° and 33°. What is the exterior angle (in degrees)?
  22. 22.In an isosceles triangle, the angle between the two equal sides is 126°. What is each of the other two angles (in degrees)?
  23. 23.In triangle ABC, angle A = 31° and angle B = 51°. What is angle C (in degrees)?
  24. 24.In a right-angled triangle, one of the other two angles is 62°. What is the third angle (in degrees)?
  25. 25.An exterior angle of a triangle is 127°. One of its two interior opposite angles is 59°. What is the other one (in degrees)?
  26. 26.The angles of a triangle are in the ratio 1 : 1 : 2. What is the smallest angle (in degrees)?
  27. 27.The angles of a triangle are in the ratio 2 : 3 : 4. What is the smallest angle (in degrees)?
  28. 28.The angles of a triangle are in the ratio 4 : 5 : 6. What is the smallest angle (in degrees)?
  29. 29.In an isosceles triangle, the angle between the two equal sides is 140°. What is each of the other two angles (in degrees)?
  30. 30.The angles of a triangle are in the ratio 1 : 2 : 2. What is the smallest angle (in degrees)?
  31. 31.The two shorter sides of a right-angled triangle are 7 cm and 24 cm. How long is the longest side (in cm)?
  32. 32.In triangle ABC, angle A = 32° and angle B = 87°. What is angle C (in degrees)?
  33. 33.An exterior angle of a triangle is 105°. One of its two interior opposite angles is 43°. What is the other one (in degrees)?
  34. 34.In an isosceles triangle, the angle between the two equal sides is 50°. What is each of the other two angles (in degrees)?
  35. 35.The two shorter sides of a right-angled triangle are 15 cm and 8 cm. How long is the longest side (in cm)?
  36. 36.In a right-angled triangle, one of the other two angles is 52°. What is the third angle (in degrees)?
  37. 37.Can a triangle have sides of 12 cm, 9 cm and 26 cm? (a) Yes (b) No
  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.The longest side of a right-angled triangle is 20 cm and one of the other sides is 12 cm. How long is the third side (in cm)?
  40. 40.In a right-angled triangle, one of the other two angles is 34°. What is the third angle (in degrees)?

Answer key

  1. 20
  2. 105
  3. 33
  4. 63
  5. No
  6. 80
  7. 75
  8. 64
  9. 21
  10. 39
  11. No
  12. 22
  13. No
  14. 100
  15. 7
  16. 76
  17. 59
  18. Yes
  19. 31
  20. 100
  21. 94
  22. 27
  23. 98
  24. 28
  25. 68
  26. 45
  27. 40
  28. 48
  29. 20
  30. 36
  31. 25
  32. 61
  33. 62
  34. 65
  35. 17
  36. 38
  37. No
  38. 24
  39. 16
  40. 56

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