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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 157 · 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 78°. What is the third angle (in degrees)?
  2. 2.The angles of a triangle are in the ratio 2 : 3 : 5. What is the smallest angle (in degrees)?
  3. 3.The angles of a triangle are in the ratio 2 : 3 : 5. What is the biggest angle (in degrees)?
  4. 4.The two shorter sides of a right-angled triangle are 8 cm and 15 cm. How long is the longest side (in cm)?
  5. 5.In an isosceles triangle, the two equal angles are 54° each. What is the third angle (in degrees)?
  6. 6.Can a triangle have sides of 17 cm, 3 cm and 10 cm? (a) Yes (b) No
  7. 7.The two shorter sides of a right-angled triangle are 24 cm and 18 cm. How long is the longest side (in cm)?
  8. 8.The two interior opposite angles of a triangle are 30° and 78°. What is the exterior angle (in degrees)?
  9. 9.In triangle ABC, angle A = 33° and angle B = 116°. What is angle C (in degrees)?
  10. 10.The longest side of a right-angled triangle is 15 cm and one of the other sides is 9 cm. How long is the third side (in cm)?
  11. 11.In a right-angled triangle, one of the other two angles is 39°. What is the third angle (in degrees)?
  12. 12.The angles of a triangle are in the ratio 1 : 2 : 2. What is the smallest angle (in degrees)?
  13. 13.An exterior angle of a triangle is 84°. One of its two interior opposite angles is 23°. What is the other one (in degrees)?
  14. 14.In an isosceles triangle, the two equal angles are 38° each. What is the third angle (in degrees)?
  15. 15.In an isosceles triangle, the angle between the two equal sides is 26°. What is each of the other two angles (in degrees)?
  16. 16.In a right-angled triangle, one of the other two angles is 49°. What is the third angle (in degrees)?
  17. 17.Can a triangle have sides of 21 cm, 8 cm and 8 cm? (a) Yes (b) No
  18. 18.The two interior opposite angles of a triangle are 29° and 41°. What is the exterior angle (in degrees)?
  19. 19.In a right-angled triangle, one of the other two angles is 75°. What is the third angle (in degrees)?
  20. 20.In triangle ABC, angle A = 44° and angle B = 43°. What is angle C (in degrees)?
  21. 21.In a right-angled triangle, one of the other two angles is 67°. What is the third angle (in degrees)?
  22. 22.In an isosceles triangle, the two equal angles are 59° each. What is the third angle (in degrees)?
  23. 23.In an isosceles triangle, the two equal angles are 60° each. What is the third angle (in degrees)?
  24. 24.In triangle ABC, angle A = 99° and angle B = 30°. What is angle C (in degrees)?
  25. 25.In an isosceles triangle, the two equal angles are 21° each. What is the third angle (in degrees)?
  26. 26.Can a triangle have sides of 21 cm, 10 cm and 10 cm? (a) No (b) Yes
  27. 27.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)?
  28. 28.In a right-angled triangle, one of the other two angles is 14°. What is the third angle (in degrees)?
  29. 29.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)?
  30. 30.The angles of a triangle are in the ratio 5 : 6 : 7. What is the smallest angle (in degrees)?
  31. 31.In a right-angled triangle, one of the other two angles is 66°. What is the third angle (in degrees)?
  32. 32.In a right-angled triangle, one of the other two angles is 12°. What is the third angle (in degrees)?
  33. 33.Can a triangle have sides of 8 cm, 6 cm and 3 cm? (a) No (b) Yes
  34. 34.In triangle ABC, angle A = 26° and angle B = 77°. What is angle C (in degrees)?
  35. 35.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)?
  36. 36.In triangle ABC, angle A = 38° and angle B = 80°. What is angle C (in degrees)?
  37. 37.Can a triangle have sides of 12 cm, 22 cm and 6 cm? (a) Yes (b) No
  38. 38.In a right-angled triangle, one of the other two angles is 61°. What is the third angle (in degrees)?
  39. 39.The two interior opposite angles of a triangle are 32° and 28°. What is the exterior angle (in degrees)?
  40. 40.In an isosceles triangle, the angle between the two equal sides is 74°. What is each of the other two angles (in degrees)?

Answer key

  1. 12
  2. 36
  3. 90
  4. 17
  5. 72
  6. No
  7. 30
  8. 108
  9. 31
  10. 12
  11. 51
  12. 36
  13. 61
  14. 104
  15. 77
  16. 41
  17. No
  18. 70
  19. 15
  20. 93
  21. 23
  22. 62
  23. 60
  24. 51
  25. 138
  26. No
  27. 12
  28. 76
  29. 15
  30. 50
  31. 24
  32. 78
  33. Yes
  34. 77
  35. 6
  36. 62
  37. No
  38. 29
  39. 60
  40. 53

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