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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 19 · 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 64°. What is the third angle (in degrees)?
  2. 2.The two shorter sides of a right-angled triangle are 15 cm and 8 cm. How long is the longest side (in cm)?
  3. 3.In an isosceles triangle, the two equal angles are 20° each. What is the third angle (in degrees)?
  4. 4.In an isosceles triangle, the two equal angles are 27° each. What is the third angle (in degrees)?
  5. 5.In a right-angled triangle, one of the other two angles is 72°. What is the third angle (in degrees)?
  6. 6.In an isosceles triangle, the two equal angles are 83° each. What is the third angle (in degrees)?
  7. 7.In triangle ABC, angle A = 66° and angle B = 90°. What is angle C (in degrees)?
  8. 8.In a right-angled triangle, one of the other two angles is 12°. What is the third angle (in degrees)?
  9. 9.In an isosceles triangle, the two equal angles are 29° each. What is the third angle (in degrees)?
  10. 10.In triangle ABC, angle A = 53° and angle B = 29°. What is angle C (in degrees)?
  11. 11.Can a triangle have sides of 2 cm, 7 cm and 7 cm? (a) Yes (b) No
  12. 12.Can a triangle have sides of 5 cm, 5 cm and 15 cm? (a) No (b) Yes
  13. 13.In triangle ABC, angle A = 99° and angle B = 29°. What is angle C (in degrees)?
  14. 14.Can a triangle have sides of 15 cm, 3 cm and 8 cm? (a) No (b) Yes
  15. 15.In a right-angled triangle, one of the other two angles is 28°. What is the third angle (in degrees)?
  16. 16.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)?
  17. 17.In a right-angled triangle, one of the other two angles is 21°. What is the third angle (in degrees)?
  18. 18.The angles of a triangle are in the ratio 2 : 3 : 5. What is the biggest angle (in degrees)?
  19. 19.In triangle ABC, angle A = 98° and angle B = 27°. What is angle C (in degrees)?
  20. 20.In an isosceles triangle, the two equal angles are 70° each. What is the third angle (in degrees)?
  21. 21.The two shorter sides of a right-angled triangle are 10 cm and 24 cm. How long is the longest side (in cm)?
  22. 22.An exterior angle of a triangle is 88°. One of its two interior opposite angles is 37°. What is the other one (in degrees)?
  23. 23.The angles of a triangle are in the ratio 1 : 1 : 2. What is the smallest angle (in degrees)?
  24. 24.Can a triangle have sides of 6 cm, 5 cm and 6 cm? (a) No (b) Yes
  25. 25.The two interior opposite angles of a triangle are 21° and 64°. What is the exterior angle (in degrees)?
  26. 26.The two interior opposite angles of a triangle are 40° and 64°. What is the exterior angle (in degrees)?
  27. 27.In triangle ABC, angle A = 46° and angle B = 81°. What is angle C (in degrees)?
  28. 28.Can a triangle have sides of 21 cm, 9 cm and 7 cm? (a) No (b) Yes
  29. 29.Can a triangle have sides of 21 cm, 6 cm and 10 cm? (a) No (b) Yes
  30. 30.In triangle ABC, angle A = 81° and angle B = 37°. What is angle C (in degrees)?
  31. 31.The longest side of a right-angled triangle is 20 cm and one of the other sides is 16 cm. How long is the third side (in cm)?
  32. 32.An exterior angle of a triangle is 72°. One of its two interior opposite angles is 28°. What is the other one (in degrees)?
  33. 33.In triangle ABC, angle A = 20° and angle B = 71°. What is angle C (in degrees)?
  34. 34.In a right-angled triangle, one of the other two angles is 60°. What is the third angle (in degrees)?
  35. 35.In triangle ABC, angle A = 100° and angle B = 55°. What is angle C (in degrees)?
  36. 36.In a right-angled triangle, one of the other two angles is 33°. What is the third angle (in degrees)?
  37. 37.An exterior angle of a triangle is 86°. One of its two interior opposite angles is 37°. What is the other one (in degrees)?
  38. 38.In an isosceles triangle, the angle between the two equal sides is 88°. What is each of the other two angles (in degrees)?
  39. 39.In a right-angled triangle, one of the other two angles is 55°. What is the third angle (in degrees)?
  40. 40.In an isosceles triangle, the two equal angles are 35° each. What is the third angle (in degrees)?

Answer key

  1. 26
  2. 17
  3. 140
  4. 126
  5. 18
  6. 14
  7. 24
  8. 78
  9. 122
  10. 98
  11. Yes
  12. No
  13. 52
  14. No
  15. 62
  16. 15
  17. 69
  18. 90
  19. 55
  20. 40
  21. 26
  22. 51
  23. 45
  24. Yes
  25. 85
  26. 104
  27. 53
  28. No
  29. No
  30. 62
  31. 12
  32. 44
  33. 89
  34. 30
  35. 25
  36. 57
  37. 49
  38. 46
  39. 35
  40. 110

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