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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 242 · 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.The angles of a triangle are in the ratio 3 : 5 : 7. What is the biggest angle (in degrees)?
  2. 2.The longest side of a right-angled triangle is 13 cm and one of the other sides is 5 cm. How long is the third side (in cm)?
  3. 3.The angles of a triangle are in the ratio 4 : 5 : 6. What is the biggest angle (in degrees)?
  4. 4.In triangle ABC, angle A = 23° and angle B = 92°. What is angle C (in degrees)?
  5. 5.In an isosceles triangle, the two equal angles are 35° each. What is the third angle (in degrees)?
  6. 6.In an isosceles triangle, the two equal angles are 26° each. What is the third angle (in degrees)?
  7. 7.The angles of a triangle are in the ratio 2 : 3 : 5. What is the biggest angle (in degrees)?
  8. 8.In triangle ABC, angle A = 22° and angle B = 31°. What is angle C (in degrees)?
  9. 9.In a right-angled triangle, one of the other two angles is 34°. What is the third angle (in degrees)?
  10. 10.In triangle ABC, angle A = 72° and angle B = 35°. What is angle C (in degrees)?
  11. 11.In a right-angled triangle, one of the other two angles is 71°. What is the third angle (in degrees)?
  12. 12.An exterior angle of a triangle is 147°. One of its two interior opposite angles is 77°. What is the other one (in degrees)?
  13. 13.The longest side of a right-angled triangle is 26 cm and one of the other sides is 10 cm. How long is the third side (in cm)?
  14. 14.In an isosceles triangle, the two equal angles are 21° each. What is the third angle (in degrees)?
  15. 15.In triangle ABC, angle A = 78° and angle B = 24°. What is angle C (in degrees)?
  16. 16.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)?
  17. 17.In triangle ABC, angle A = 79° and angle B = 75°. What is angle C (in degrees)?
  18. 18.Can a triangle have sides of 3 cm, 4 cm and 4 cm? (a) Yes (b) No
  19. 19.The angles of a triangle are in the ratio 5 : 6 : 7. What is the biggest angle (in degrees)?
  20. 20.In triangle ABC, angle A = 63° and angle B = 55°. What is angle C (in degrees)?
  21. 21.In triangle ABC, angle A = 56° and angle B = 97°. What is angle C (in degrees)?
  22. 22.In triangle ABC, angle A = 39° and angle B = 58°. What is angle C (in degrees)?
  23. 23.In a right-angled triangle, one of the other two angles is 43°. What is the third angle (in degrees)?
  24. 24.In a right-angled triangle, one of the other two angles is 39°. What is the third angle (in degrees)?
  25. 25.In an isosceles triangle, the two equal angles are 40° each. What is the third angle (in degrees)?
  26. 26.The angles of a triangle are in the ratio 3 : 3 : 4. What is the smallest angle (in degrees)?
  27. 27.The two shorter sides of a right-angled triangle are 8 cm and 15 cm. How long is the longest side (in cm)?
  28. 28.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)?
  29. 29.Can a triangle have sides of 23 cm, 10 cm and 9 cm? (a) No (b) Yes
  30. 30.Can a triangle have sides of 10 cm, 11 cm and 15 cm? (a) No (b) Yes
  31. 31.In a right-angled triangle, one of the other two angles is 73°. What is the third angle (in degrees)?
  32. 32.In a right-angled triangle, one of the other two angles is 29°. What is the third angle (in degrees)?
  33. 33.An exterior angle of a triangle is 59°. One of its two interior opposite angles is 26°. What is the other one (in degrees)?
  34. 34.In an isosceles triangle, the two equal angles are 39° each. What is the third angle (in degrees)?
  35. 35.The two interior opposite angles of a triangle are 42° and 74°. What is the exterior angle (in degrees)?
  36. 36.Can a triangle have sides of 13 cm, 10 cm and 5 cm? (a) Yes (b) No
  37. 37.In triangle ABC, angle A = 39° and angle B = 36°. What is angle C (in degrees)?
  38. 38.The angles of a triangle are in the ratio 2 : 2 : 5. What is the biggest angle (in degrees)?
  39. 39.In an isosceles triangle, the angle between the two equal sides is 30°. What is each of the other two angles (in degrees)?
  40. 40.In triangle ABC, angle A = 73° and angle B = 79°. What is angle C (in degrees)?

Answer key

  1. 84
  2. 12
  3. 72
  4. 65
  5. 110
  6. 128
  7. 90
  8. 127
  9. 56
  10. 73
  11. 19
  12. 70
  13. 24
  14. 138
  15. 78
  16. 15
  17. 26
  18. Yes
  19. 70
  20. 62
  21. 27
  22. 83
  23. 47
  24. 51
  25. 100
  26. 54
  27. 17
  28. 15
  29. No
  30. Yes
  31. 17
  32. 61
  33. 33
  34. 102
  35. 116
  36. Yes
  37. 105
  38. 100
  39. 75
  40. 28

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