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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 37 · 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 37°. What is the third angle (in degrees)?
  2. 2.The angles of a triangle are in the ratio 1 : 2 : 3. What is the biggest angle (in degrees)?
  3. 3.The angles of a triangle are in the ratio 1 : 4 : 5. What is the biggest angle (in degrees)?
  4. 4.The angles of a triangle are in the ratio 3 : 5 : 7. What is the biggest angle (in degrees)?
  5. 5.In an isosceles triangle, the two equal angles are 39° each. What is the third angle (in degrees)?
  6. 6.The longest side of a right-angled triangle is 39 cm and one of the other sides is 15 cm. How long is the third side (in cm)?
  7. 7.In an isosceles triangle, the angle between the two equal sides is 92°. What is each of the other two angles (in degrees)?
  8. 8.The two shorter sides of a right-angled triangle are 8 cm and 15 cm. How long is the longest side (in cm)?
  9. 9.An exterior angle of a triangle is 117°. One of its two interior opposite angles is 74°. What is the other one (in degrees)?
  10. 10.The longest side of a right-angled triangle is 25 cm and one of the other sides is 24 cm. How long is the third side (in cm)?
  11. 11.The two shorter sides of a right-angled triangle are 3 cm and 4 cm. How long is the longest side (in cm)?
  12. 12.An exterior angle of a triangle is 67°. One of its two interior opposite angles is 26°. What is the other one (in degrees)?
  13. 13.An exterior angle of a triangle is 68°. One of its two interior opposite angles is 44°. What is the other one (in degrees)?
  14. 14.In a right-angled triangle, one of the other two angles is 57°. What is the third angle (in degrees)?
  15. 15.Can a triangle have sides of 10 cm, 9 cm and 10 cm? (a) No (b) Yes
  16. 16.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)?
  17. 17.In an isosceles triangle, the two equal angles are 71° each. What is the third angle (in degrees)?
  18. 18.In a right-angled triangle, one of the other two angles is 43°. What is the third angle (in degrees)?
  19. 19.In triangle ABC, angle A = 23° and angle B = 65°. What is angle C (in degrees)?
  20. 20.In triangle ABC, angle A = 89° and angle B = 57°. What is angle C (in degrees)?
  21. 21.Can a triangle have sides of 3 cm, 3 cm and 11 cm? (a) No (b) Yes
  22. 22.In an isosceles triangle, the two equal angles are 28° each. What is the third angle (in degrees)?
  23. 23.In a right-angled triangle, one of the other two angles is 65°. What is the third angle (in degrees)?
  24. 24.In triangle ABC, angle A = 36° and angle B = 68°. What is angle C (in degrees)?
  25. 25.In triangle ABC, angle A = 71° and angle B = 67°. What is angle C (in degrees)?
  26. 26.In a right-angled triangle, one of the other two angles is 71°. What is the third angle (in degrees)?
  27. 27.In a right-angled triangle, one of the other two angles is 29°. What is the third angle (in degrees)?
  28. 28.The angles of a triangle are in the ratio 2 : 3 : 4. What is the smallest angle (in degrees)?
  29. 29.Can a triangle have sides of 8 cm, 11 cm and 5 cm? (a) Yes (b) No
  30. 30.The two interior opposite angles of a triangle are 68° and 65°. What is the exterior angle (in degrees)?
  31. 31.In a right-angled triangle, one of the other two angles is 76°. What is the third angle (in degrees)?
  32. 32.In triangle ABC, angle A = 85° and angle B = 72°. What is angle C (in degrees)?
  33. 33.Can a triangle have sides of 7 cm, 11 cm and 4 cm? (a) No (b) Yes
  34. 34.In triangle ABC, angle A = 47° and angle B = 53°. What is angle C (in degrees)?
  35. 35.In triangle ABC, angle A = 76° and angle B = 39°. What is angle C (in degrees)?
  36. 36.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)?
  37. 37.The angles of a triangle are in the ratio 2 : 3 : 5. What is the smallest angle (in degrees)?
  38. 38.An exterior angle of a triangle is 135°. One of its two interior opposite angles is 70°. What is the other one (in degrees)?
  39. 39.In an isosceles triangle, the two equal angles are 44° each. What is the third angle (in degrees)?
  40. 40.In an isosceles triangle, the angle between the two equal sides is 42°. What is each of the other two angles (in degrees)?

Answer key

  1. 53
  2. 90
  3. 90
  4. 84
  5. 102
  6. 36
  7. 44
  8. 17
  9. 43
  10. 7
  11. 5
  12. 41
  13. 24
  14. 33
  15. Yes
  16. 8
  17. 38
  18. 47
  19. 92
  20. 34
  21. No
  22. 124
  23. 25
  24. 76
  25. 42
  26. 19
  27. 61
  28. 40
  29. Yes
  30. 133
  31. 14
  32. 23
  33. No
  34. 80
  35. 65
  36. 15
  37. 36
  38. 65
  39. 92
  40. 69

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