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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 8 · 40 sums
TalentJR

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 47°. What is the third angle (in degrees)?
  2. 2.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)?
  3. 3.In triangle ABC, angle A = 50° and angle B = 50°. What is angle C (in degrees)?
  4. 4.In triangle ABC, angle A = 54° and angle B = 85°. What is angle C (in degrees)?
  5. 5.In an isosceles triangle, the two equal angles are 84° each. What is the third angle (in degrees)?
  6. 6.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)?
  7. 7.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)?
  8. 8.The two interior opposite angles of a triangle are 54° and 58°. What is the exterior angle (in degrees)?
  9. 9.In a right-angled triangle, one of the other two angles is 54°. What is the third angle (in degrees)?
  10. 10.The two interior opposite angles of a triangle are 35° and 47°. 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 8 cm. How long is the third side (in cm)?
  12. 12.In triangle ABC, angle A = 54° and angle B = 86°. What is angle C (in degrees)?
  13. 13.The two shorter sides of a right-angled triangle are 8 cm and 15 cm. How long is the longest side (in cm)?
  14. 14.Can a triangle have sides of 6 cm, 4 cm and 14 cm? (a) No (b) Yes
  15. 15.In a right-angled triangle, one of the other two angles is 66°. What is the third angle (in degrees)?
  16. 16.The two interior opposite angles of a triangle are 36° and 37°. What is the exterior angle (in degrees)?
  17. 17.In an isosceles triangle, the angle between the two equal sides is 58°. What is each of the other two angles (in degrees)?
  18. 18.In an isosceles triangle, the two equal angles are 20° each. What is the third angle (in degrees)?
  19. 19.The two interior opposite angles of a triangle are 61° and 40°. What is the exterior angle (in degrees)?
  20. 20.Can a triangle have sides of 9 cm, 21 cm and 7 cm? (a) Yes (b) No
  21. 21.The two interior opposite angles of a triangle are 72° and 73°. What is the exterior angle (in degrees)?
  22. 22.In triangle ABC, angle A = 34° and angle B = 85°. What is angle C (in degrees)?
  23. 23.In a right-angled triangle, one of the other two angles is 11°. What is the third angle (in degrees)?
  24. 24.In an isosceles triangle, the two equal angles are 65° each. What is the third angle (in degrees)?
  25. 25.In triangle ABC, angle A = 58° and angle B = 31°. What is angle C (in degrees)?
  26. 26.The two interior opposite angles of a triangle are 54° and 36°. What is the exterior angle (in degrees)?
  27. 27.In triangle ABC, angle A = 72° and angle B = 67°. What is angle C (in degrees)?
  28. 28.Can a triangle have sides of 12 cm, 5 cm and 13 cm? (a) Yes (b) No
  29. 29.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)?
  30. 30.In an isosceles triangle, the angle between the two equal sides is 142°. What is each of the other two angles (in degrees)?
  31. 31.In an isosceles triangle, the two equal angles are 81° each. What is the third angle (in degrees)?
  32. 32.In an isosceles triangle, the two equal angles are 57° each. What is the third angle (in degrees)?
  33. 33.The angles of a triangle are in the ratio 5 : 6 : 7. What is the smallest angle (in degrees)?
  34. 34.In a right-angled triangle, one of the other two angles is 42°. What is the third angle (in degrees)?
  35. 35.In a right-angled triangle, one of the other two angles is 10°. What is the third angle (in degrees)?
  36. 36.In a right-angled triangle, one of the other two angles is 21°. What is the third angle (in degrees)?
  37. 37.The two shorter sides of a right-angled triangle are 24 cm and 7 cm. How long is the longest side (in cm)?
  38. 38.An exterior angle of a triangle is 74°. One of its two interior opposite angles is 50°. What is the other one (in degrees)?
  39. 39.Can a triangle have sides of 8 cm, 8 cm and 8 cm? (a) Yes (b) No
  40. 40.An exterior angle of a triangle is 143°. One of its two interior opposite angles is 69°. What is the other one (in degrees)?

Answer key

  1. 43
  2. 24
  3. 80
  4. 41
  5. 12
  6. 15
  7. 8
  8. 112
  9. 36
  10. 82
  11. 6
  12. 40
  13. 17
  14. No
  15. 24
  16. 73
  17. 61
  18. 140
  19. 101
  20. No
  21. 145
  22. 61
  23. 79
  24. 50
  25. 91
  26. 90
  27. 41
  28. Yes
  29. 8
  30. 19
  31. 18
  32. 66
  33. 50
  34. 48
  35. 80
  36. 69
  37. 25
  38. 24
  39. Yes
  40. 74

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