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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 330 · 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.An exterior angle of a triangle is 129°. One of its two interior opposite angles is 78°. What is the other one (in degrees)?
  2. 2.In a right-angled triangle, one of the other two angles is 45°. What is the third angle (in degrees)?
  3. 3.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)?
  4. 4.The angles of a triangle are in the ratio 1 : 1 : 2. What is the biggest angle (in degrees)?
  5. 5.In triangle ABC, angle A = 56° and angle B = 49°. What is angle C (in degrees)?
  6. 6.An exterior angle of a triangle is 125°. One of its two interior opposite angles is 55°. What is the other one (in degrees)?
  7. 7.The two shorter sides of a right-angled triangle are 15 cm and 8 cm. How long is the longest side (in cm)?
  8. 8.Can a triangle have sides of 9 cm, 4 cm and 9 cm? (a) No (b) Yes
  9. 9.In a right-angled triangle, one of the other two angles is 24°. What is the third angle (in degrees)?
  10. 10.In a right-angled triangle, one of the other two angles is 22°. What is the third angle (in degrees)?
  11. 11.In triangle ABC, angle A = 22° and angle B = 28°. What is angle C (in degrees)?
  12. 12.In a right-angled triangle, one of the other two angles is 34°. What is the third angle (in degrees)?
  13. 13.The two interior opposite angles of a triangle are 65° and 52°. What is the exterior angle (in degrees)?
  14. 14.In an isosceles triangle, the angle between the two equal sides is 94°. What is each of the other two angles (in degrees)?
  15. 15.The angles of a triangle are in the ratio 5 : 6 : 7. What is the biggest angle (in degrees)?
  16. 16.The angles of a triangle are in the ratio 1 : 2 : 3. What is the biggest angle (in degrees)?
  17. 17.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)?
  18. 18.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)?
  19. 19.In triangle ABC, angle A = 27° and angle B = 29°. What is angle C (in degrees)?
  20. 20.In triangle ABC, angle A = 58° and angle B = 81°. What is angle C (in degrees)?
  21. 21.The two interior opposite angles of a triangle are 63° and 57°. What is the exterior angle (in degrees)?
  22. 22.In triangle ABC, angle A = 23° and angle B = 79°. What is angle C (in degrees)?
  23. 23.In a right-angled triangle, one of the other two angles is 12°. What is the third angle (in degrees)?
  24. 24.In an isosceles triangle, the two equal angles are 38° each. What is the third angle (in degrees)?
  25. 25.Can a triangle have sides of 21 cm, 11 cm and 10 cm? (a) No (b) Yes
  26. 26.In triangle ABC, angle A = 68° and angle B = 84°. What is angle C (in degrees)?
  27. 27.An exterior angle of a triangle is 98°. One of its two interior opposite angles is 71°. What is the other one (in degrees)?
  28. 28.Can a triangle have sides of 5 cm, 9 cm and 9 cm? (a) No (b) Yes
  29. 29.In a right-angled triangle, one of the other two angles is 36°. What is the third angle (in degrees)?
  30. 30.The longest side of a right-angled triangle is 39 cm and one of the other sides is 36 cm. How long is the third side (in cm)?
  31. 31.In a right-angled triangle, one of the other two angles is 26°. What is the third angle (in degrees)?
  32. 32.In triangle ABC, angle A = 49° and angle B = 69°. What is angle C (in degrees)?
  33. 33.The two interior opposite angles of a triangle are 59° and 69°. What is the exterior angle (in degrees)?
  34. 34.The two interior opposite angles of a triangle are 41° and 24°. What is the exterior angle (in degrees)?
  35. 35.In a right-angled triangle, one of the other two angles is 17°. What is the third angle (in degrees)?
  36. 36.The two interior opposite angles of a triangle are 32° and 79°. What is the exterior angle (in degrees)?
  37. 37.The angles of a triangle are in the ratio 2 : 7 : 9. What is the biggest angle (in degrees)?
  38. 38.The angles of a triangle are in the ratio 1 : 2 : 6. What is the biggest angle (in degrees)?
  39. 39.In a right-angled triangle, one of the other two angles is 59°. What is the third angle (in degrees)?
  40. 40.In an isosceles triangle, the angle between the two equal sides is 54°. What is each of the other two angles (in degrees)?

Answer key

  1. 51
  2. 45
  3. 8
  4. 90
  5. 75
  6. 70
  7. 17
  8. Yes
  9. 66
  10. 68
  11. 130
  12. 56
  13. 117
  14. 43
  15. 70
  16. 90
  17. 3
  18. 8
  19. 124
  20. 41
  21. 120
  22. 78
  23. 78
  24. 104
  25. No
  26. 28
  27. 27
  28. Yes
  29. 54
  30. 15
  31. 64
  32. 62
  33. 128
  34. 65
  35. 73
  36. 111
  37. 90
  38. 120
  39. 31
  40. 63

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