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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 159 · 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 triangle ABC, angle A = 39° and angle B = 55°. What is angle C (in degrees)?
  2. 2.In triangle ABC, angle A = 79° and angle B = 20°. What is angle C (in degrees)?
  3. 3.In an isosceles triangle, the angle between the two equal sides is 42°. What is each of the other two angles (in degrees)?
  4. 4.The angles of a triangle are in the ratio 1 : 1 : 2. What is the biggest angle (in degrees)?
  5. 5.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)?
  6. 6.The two shorter sides of a right-angled triangle are 8 cm and 15 cm. How long is the longest side (in cm)?
  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.The angles of a triangle are in the ratio 2 : 2 : 5. What is the smallest 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 an isosceles triangle, the angle between the two equal sides is 94°. What is each of the other two angles (in degrees)?
  11. 11.Can a triangle have sides of 8 cm, 6 cm and 16 cm? (a) No (b) Yes
  12. 12.Can a triangle have sides of 7 cm, 3 cm and 3 cm? (a) No (b) Yes
  13. 13.Can a triangle have sides of 9 cm, 22 cm and 12 cm? (a) No (b) Yes
  14. 14.In a right-angled triangle, one of the other two angles is 23°. What is the third angle (in degrees)?
  15. 15.In a right-angled triangle, one of the other two angles is 26°. What is the third angle (in degrees)?
  16. 16.In an isosceles triangle, the two equal angles are 23° each. What is the third angle (in degrees)?
  17. 17.In a right-angled triangle, one of the other two angles is 67°. What is the third angle (in degrees)?
  18. 18.Can a triangle have sides of 7 cm, 7 cm and 2 cm? (a) No (b) Yes
  19. 19.The angles of a triangle are in the ratio 1 : 2 : 3. What is the smallest angle (in degrees)?
  20. 20.In triangle ABC, angle A = 34° and angle B = 81°. What is angle C (in degrees)?
  21. 21.An exterior angle of a triangle is 77°. One of its two interior opposite angles is 33°. What is the other one (in degrees)?
  22. 22.The two interior opposite angles of a triangle are 66° and 33°. What is the exterior angle (in degrees)?
  23. 23.In triangle ABC, angle A = 77° and angle B = 30°. What is angle C (in degrees)?
  24. 24.Can a triangle have sides of 18 cm, 12 cm and 3 cm? (a) No (b) Yes
  25. 25.In an isosceles triangle, the two equal angles are 72° each. What is the third angle (in degrees)?
  26. 26.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)?
  27. 27.Can a triangle have sides of 5 cm, 8 cm and 16 cm? (a) Yes (b) No
  28. 28.In a right-angled triangle, one of the other two angles is 51°. What is the third angle (in degrees)?
  29. 29.In a right-angled triangle, one of the other two angles is 55°. What is the third angle (in degrees)?
  30. 30.The angles of a triangle are in the ratio 4 : 5 : 6. What is the smallest angle (in degrees)?
  31. 31.The angles of a triangle are in the ratio 3 : 5 : 7. What is the biggest angle (in degrees)?
  32. 32.In an isosceles triangle, the angle between the two equal sides is 150°. What is each of the other two angles (in degrees)?
  33. 33.In an isosceles triangle, the angle between the two equal sides is 56°. What is each of the other two angles (in degrees)?
  34. 34.Can a triangle have sides of 10 cm, 6 cm and 6 cm? (a) No (b) Yes
  35. 35.In triangle ABC, angle A = 30° and angle B = 116°. What is angle C (in degrees)?
  36. 36.The angles of a triangle are in the ratio 5 : 6 : 7. What is the biggest angle (in degrees)?
  37. 37.In an isosceles triangle, the angle between the two equal sides is 126°. What is each of the other two angles (in degrees)?
  38. 38.The two shorter sides of a right-angled triangle are 7 cm and 24 cm. How long is the longest side (in cm)?
  39. 39.The two interior opposite angles of a triangle are 73° and 70°. What is the exterior angle (in degrees)?
  40. 40.In an isosceles triangle, the two equal angles are 60° each. What is the third angle (in degrees)?

Answer key

  1. 86
  2. 81
  3. 69
  4. 90
  5. 7
  6. 17
  7. 17
  8. 40
  9. 122
  10. 43
  11. No
  12. No
  13. No
  14. 67
  15. 64
  16. 134
  17. 23
  18. Yes
  19. 30
  20. 65
  21. 44
  22. 99
  23. 73
  24. No
  25. 36
  26. 15
  27. No
  28. 39
  29. 35
  30. 48
  31. 84
  32. 15
  33. 62
  34. Yes
  35. 34
  36. 70
  37. 27
  38. 25
  39. 143
  40. 60

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