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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 766 · 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.An exterior angle of a triangle is 56°. One of its two interior opposite angles is 22°. What is the other one (in degrees)?
  2. 2.Can a triangle have sides of 3 cm, 12 cm and 20 cm? (a) Yes (b) No
  3. 3.The two interior opposite angles of a triangle are 20° and 53°. What is the exterior angle (in degrees)?
  4. 4.An exterior angle of a triangle is 73°. One of its two interior opposite angles is 51°. What is the other one (in degrees)?
  5. 5.The two interior opposite angles of a triangle are 61° and 58°. What is the exterior angle (in degrees)?
  6. 6.In a right-angled triangle, one of the other two angles is 66°. What is the third angle (in degrees)?
  7. 7.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)?
  8. 8.In an isosceles triangle, the two equal angles are 53° each. What is the third angle (in degrees)?
  9. 9.The angles of a triangle are in the ratio 2 : 3 : 4. What is the smallest angle (in degrees)?
  10. 10.The two interior opposite angles of a triangle are 43° and 62°. What is the exterior angle (in degrees)?
  11. 11.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)?
  12. 12.In triangle ABC, angle A = 82° and angle B = 54°. What is angle C (in degrees)?
  13. 13.In an isosceles triangle, the angle between the two equal sides is 30°. What is each of the other two angles (in degrees)?
  14. 14.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)?
  15. 15.In triangle ABC, angle A = 51° and angle B = 80°. What is angle C (in degrees)?
  16. 16.The two interior opposite angles of a triangle are 29° and 33°. What is the exterior angle (in degrees)?
  17. 17.In a right-angled triangle, one of the other two angles is 69°. What is the third angle (in degrees)?
  18. 18.In a right-angled triangle, one of the other two angles is 12°. What is the third angle (in degrees)?
  19. 19.The angles of a triangle are in the ratio 3 : 3 : 4. What is the smallest angle (in degrees)?
  20. 20.The angles of a triangle are in the ratio 1 : 3 : 5. What is the smallest angle (in degrees)?
  21. 21.Can a triangle have sides of 3 cm, 10 cm and 14 cm? (a) Yes (b) No
  22. 22.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)?
  23. 23.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)?
  24. 24.In an isosceles triangle, the two equal angles are 66° each. What is the third angle (in degrees)?
  25. 25.The two interior opposite angles of a triangle are 75° and 34°. What is the exterior angle (in degrees)?
  26. 26.In an isosceles triangle, the angle between the two equal sides is 134°. What is each of the other two angles (in degrees)?
  27. 27.Can a triangle have sides of 11 cm, 22 cm and 9 cm? (a) Yes (b) No
  28. 28.In an isosceles triangle, the angle between the two equal sides is 140°. What is each of the other two angles (in degrees)?
  29. 29.The angles of a triangle are in the ratio 2 : 2 : 5. What is the smallest angle (in degrees)?
  30. 30.The two shorter sides of a right-angled triangle are 15 cm and 8 cm. How long is the longest side (in cm)?
  31. 31.An exterior angle of a triangle is 93°. One of its two interior opposite angles is 58°. What is the other one (in degrees)?
  32. 32.The longest side of a right-angled triangle is 17 cm and one of the other sides is 15 cm. How long is the third side (in cm)?
  33. 33.In triangle ABC, angle A = 74° and angle B = 76°. What is angle C (in degrees)?
  34. 34.The angles of a triangle are in the ratio 3 : 5 : 7. What is the smallest angle (in degrees)?
  35. 35.The two interior opposite angles of a triangle are 58° and 37°. What is the exterior angle (in degrees)?
  36. 36.In a right-angled triangle, one of the other two angles is 14°. What is the third angle (in degrees)?
  37. 37.In triangle ABC, angle A = 21° and angle B = 34°. What is angle C (in degrees)?
  38. 38.The angles of a triangle are in the ratio 4 : 5 : 6. What is the biggest angle (in degrees)?
  39. 39.Can a triangle have sides of 12 cm, 11 cm and 4 cm? (a) No (b) Yes
  40. 40.In triangle ABC, angle A = 54° and angle B = 56°. What is angle C (in degrees)?

Answer key

  1. 34
  2. No
  3. 73
  4. 22
  5. 119
  6. 24
  7. 15
  8. 74
  9. 40
  10. 105
  11. 8
  12. 44
  13. 75
  14. 7
  15. 49
  16. 62
  17. 21
  18. 78
  19. 54
  20. 20
  21. No
  22. 24
  23. 3
  24. 48
  25. 109
  26. 23
  27. No
  28. 20
  29. 40
  30. 17
  31. 35
  32. 8
  33. 30
  34. 36
  35. 95
  36. 76
  37. 125
  38. 72
  39. Yes
  40. 70

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