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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 127 · 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 = 42° and angle B = 66°. What is angle C (in degrees)?
  2. 2.In a right-angled triangle, one of the other two angles is 63°. What is the third angle (in degrees)?
  3. 3.In a right-angled triangle, one of the other two angles is 12°. What is the third angle (in degrees)?
  4. 4.The two interior opposite angles of a triangle are 50° and 78°. What is the exterior angle (in degrees)?
  5. 5.Can a triangle have sides of 4 cm, 2 cm and 5 cm? (a) No (b) Yes
  6. 6.Can a triangle have sides of 16 cm, 4 cm and 11 cm? (a) Yes (b) No
  7. 7.In a right-angled triangle, one of the other two angles is 45°. What is the third angle (in degrees)?
  8. 8.In an isosceles triangle, the angle between the two equal sides is 152°. What is each of the other two angles (in degrees)?
  9. 9.In triangle ABC, angle A = 23° and angle B = 131°. What is angle C (in degrees)?
  10. 10.In a right-angled triangle, one of the other two angles is 53°. What is the third angle (in degrees)?
  11. 11.In triangle ABC, angle A = 20° and angle B = 34°. What is angle C (in degrees)?
  12. 12.In an isosceles triangle, the two equal angles are 26° each. What is the third angle (in degrees)?
  13. 13.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)?
  14. 14.The angles of a triangle are in the ratio 1 : 2 : 6. What is the biggest angle (in degrees)?
  15. 15.In triangle ABC, angle A = 47° and angle B = 28°. What is angle C (in degrees)?
  16. 16.An exterior angle of a triangle is 144°. One of its two interior opposite angles is 77°. What is the other one (in degrees)?
  17. 17.In triangle ABC, angle A = 22° and angle B = 35°. What is angle C (in degrees)?
  18. 18.The two shorter sides of a right-angled triangle are 15 cm and 8 cm. How long is the longest side (in cm)?
  19. 19.In a right-angled triangle, one of the other two angles is 40°. What is the third angle (in degrees)?
  20. 20.In triangle ABC, angle A = 50° and angle B = 71°. What is angle C (in degrees)?
  21. 21.In a right-angled triangle, one of the other two angles is 62°. What is the third angle (in degrees)?
  22. 22.An exterior angle of a triangle is 107°. One of its two interior opposite angles is 52°. What is the other one (in degrees)?
  23. 23.In triangle ABC, angle A = 89° and angle B = 66°. What is angle C (in degrees)?
  24. 24.In a right-angled triangle, one of the other two angles is 25°. What is the third angle (in degrees)?
  25. 25.In triangle ABC, angle A = 41° and angle B = 102°. What is angle C (in degrees)?
  26. 26.The two shorter sides of a right-angled triangle are 24 cm and 10 cm. How long is the longest side (in cm)?
  27. 27.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)?
  28. 28.The two shorter sides of a right-angled triangle are 9 cm and 12 cm. How long is the longest side (in cm)?
  29. 29.The two shorter sides of a right-angled triangle are 8 cm and 6 cm. How long is the longest side (in cm)?
  30. 30.In a right-angled triangle, one of the other two angles is 15°. What is the third angle (in degrees)?
  31. 31.The two shorter sides of a right-angled triangle are 4 cm and 3 cm. How long is the longest side (in cm)?
  32. 32.The two shorter sides of a right-angled triangle are 12 cm and 9 cm. How long is the longest side (in cm)?
  33. 33.Can a triangle have sides of 3 cm, 3 cm and 2 cm? (a) No (b) Yes
  34. 34.Can a triangle have sides of 8 cm, 8 cm and 20 cm? (a) No (b) Yes
  35. 35.The two interior opposite angles of a triangle are 63° and 34°. What is the exterior angle (in degrees)?
  36. 36.Can a triangle have sides of 4 cm, 12 cm and 7 cm? (a) Yes (b) No
  37. 37.The angles of a triangle are in the ratio 3 : 3 : 4. What is the smallest angle (in degrees)?
  38. 38.In a right-angled triangle, one of the other two angles is 23°. What is the third angle (in degrees)?
  39. 39.In an isosceles triangle, the angle between the two equal sides is 98°. What is each of the other two angles (in degrees)?
  40. 40.In an isosceles triangle, the two equal angles are 81° each. What is the third angle (in degrees)?

Answer key

  1. 72
  2. 27
  3. 78
  4. 128
  5. Yes
  6. No
  7. 45
  8. 14
  9. 26
  10. 37
  11. 126
  12. 128
  13. 7
  14. 120
  15. 105
  16. 67
  17. 123
  18. 17
  19. 50
  20. 59
  21. 28
  22. 55
  23. 25
  24. 65
  25. 37
  26. 26
  27. 36
  28. 15
  29. 10
  30. 75
  31. 5
  32. 15
  33. Yes
  34. No
  35. 97
  36. No
  37. 54
  38. 67
  39. 41
  40. 18

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