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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 537 · 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.An exterior angle of a triangle is 78°. One of its two interior opposite angles is 50°. What is the other one (in degrees)?
  2. 2.In triangle ABC, angle A = 43° and angle B = 72°. What is angle C (in degrees)?
  3. 3.The angles of a triangle are in the ratio 1 : 2 : 3. What is the smallest angle (in degrees)?
  4. 4.In a right-angled triangle, one of the other two angles is 69°. What is the third angle (in degrees)?
  5. 5.The angles of a triangle are in the ratio 3 : 3 : 4. What is the biggest angle (in degrees)?
  6. 6.The two shorter sides of a right-angled triangle are 7 cm and 24 cm. How long is the longest side (in cm)?
  7. 7.In triangle ABC, angle A = 31° and angle B = 41°. What is angle C (in degrees)?
  8. 8.In triangle ABC, angle A = 75° and angle B = 42°. What is angle C (in degrees)?
  9. 9.An exterior angle of a triangle is 145°. One of its two interior opposite angles is 76°. What is the other one (in degrees)?
  10. 10.An exterior angle of a triangle is 130°. One of its two interior opposite angles is 54°. What is the other one (in degrees)?
  11. 11.In a right-angled triangle, one of the other two angles is 74°. What is the third angle (in degrees)?
  12. 12.In triangle ABC, angle A = 84° and angle B = 75°. What is angle C (in degrees)?
  13. 13.In triangle ABC, angle A = 31° and angle B = 61°. What is angle C (in degrees)?
  14. 14.In triangle ABC, angle A = 100° and angle B = 35°. What is angle C (in degrees)?
  15. 15.The two interior opposite angles of a triangle are 56° and 42°. What is the exterior angle (in degrees)?
  16. 16.The two shorter sides of a right-angled triangle are 3 cm and 4 cm. How long is the longest side (in cm)?
  17. 17.The two interior opposite angles of a triangle are 20° and 71°. What is the exterior angle (in degrees)?
  18. 18.In a right-angled triangle, one of the other two angles is 49°. What is the third angle (in degrees)?
  19. 19.In an isosceles triangle, the angle between the two equal sides is 50°. What is each of the other two angles (in degrees)?
  20. 20.In triangle ABC, angle A = 43° and angle B = 33°. What is angle C (in degrees)?
  21. 21.Can a triangle have sides of 5 cm, 13 cm and 8 cm? (a) Yes (b) No
  22. 22.An exterior angle of a triangle is 111°. One of its two interior opposite angles is 66°. What is the other one (in degrees)?
  23. 23.The two interior opposite angles of a triangle are 71° and 65°. What is the exterior angle (in degrees)?
  24. 24.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)?
  25. 25.The longest side of a right-angled triangle is 25 cm and one of the other sides is 7 cm. How long is the third side (in cm)?
  26. 26.An exterior angle of a triangle is 98°. One of its two interior opposite angles is 29°. What is the other one (in degrees)?
  27. 27.Can a triangle have sides of 2 cm, 2 cm and 9 cm? (a) No (b) Yes
  28. 28.The two interior opposite angles of a triangle are 56° and 68°. What is the exterior angle (in degrees)?
  29. 29.Can a triangle have sides of 3 cm, 4 cm and 5 cm? (a) Yes (b) No
  30. 30.Can a triangle have sides of 5 cm, 7 cm and 2 cm? (a) Yes (b) No
  31. 31.The angles of a triangle are in the ratio 2 : 7 : 9. What is the smallest angle (in degrees)?
  32. 32.The angles of a triangle are in the ratio 2 : 7 : 9. What is the biggest angle (in degrees)?
  33. 33.The two interior opposite angles of a triangle are 64° and 64°. What is the exterior angle (in degrees)?
  34. 34.In triangle ABC, angle A = 70° and angle B = 69°. What is angle C (in degrees)?
  35. 35.In triangle ABC, angle A = 28° and angle B = 27°. What is angle C (in degrees)?
  36. 36.The longest side of a right-angled triangle is 5 cm and one of the other sides is 4 cm. How long is the third side (in cm)?
  37. 37.Can a triangle have sides of 18 cm, 12 cm and 3 cm? (a) Yes (b) No
  38. 38.The angles of a triangle are in the ratio 3 : 5 : 7. What is the smallest angle (in degrees)?
  39. 39.In triangle ABC, angle A = 87° and angle B = 39°. What is angle C (in degrees)?
  40. 40.The two interior opposite angles of a triangle are 56° and 24°. What is the exterior angle (in degrees)?

Answer key

  1. 28
  2. 65
  3. 30
  4. 21
  5. 72
  6. 25
  7. 108
  8. 63
  9. 69
  10. 76
  11. 16
  12. 21
  13. 88
  14. 45
  15. 98
  16. 5
  17. 91
  18. 41
  19. 65
  20. 104
  21. No
  22. 45
  23. 136
  24. 15
  25. 24
  26. 69
  27. No
  28. 124
  29. Yes
  30. No
  31. 20
  32. 90
  33. 128
  34. 41
  35. 125
  36. 3
  37. No
  38. 36
  39. 54
  40. 80

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