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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 314 · 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.The longest side of a right-angled triangle is 15 cm and one of the other sides is 12 cm. How long is the third side (in cm)?
  2. 2.In a right-angled triangle, one of the other two angles is 79°. What is the third angle (in degrees)?
  3. 3.In an isosceles triangle, the angle between the two equal sides is 38°. What is each of the other two angles (in degrees)?
  4. 4.The angles of a triangle are in the ratio 2 : 3 : 4. What is the smallest angle (in degrees)?
  5. 5.In triangle ABC, angle A = 49° and angle B = 110°. What is angle C (in degrees)?
  6. 6.In a right-angled triangle, one of the other two angles is 13°. What is the third angle (in degrees)?
  7. 7.The two interior opposite angles of a triangle are 66° and 20°. What is the exterior angle (in degrees)?
  8. 8.The angles of a triangle are in the ratio 1 : 4 : 5. What is the smallest angle (in degrees)?
  9. 9.The angles of a triangle are in the ratio 1 : 1 : 2. What is the biggest angle (in degrees)?
  10. 10.In a right-angled triangle, one of the other two angles is 28°. What is the third angle (in degrees)?
  11. 11.In triangle ABC, angle A = 24° and angle B = 38°. What is angle C (in degrees)?
  12. 12.An exterior angle of a triangle is 102°. One of its two interior opposite angles is 44°. What is the other one (in degrees)?
  13. 13.The two shorter sides of a right-angled triangle are 5 cm and 12 cm. How long is the longest side (in cm)?
  14. 14.In triangle ABC, angle A = 32° and angle B = 110°. What is angle C (in degrees)?
  15. 15.In triangle ABC, angle A = 82° and angle B = 67°. What is angle C (in degrees)?
  16. 16.Can a triangle have sides of 10 cm, 17 cm and 4 cm? (a) Yes (b) No
  17. 17.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)?
  18. 18.In a right-angled triangle, one of the other two angles is 23°. What is the third angle (in degrees)?
  19. 19.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)?
  20. 20.Can a triangle have sides of 4 cm, 4 cm and 3 cm? (a) No (b) Yes
  21. 21.The two shorter sides of a right-angled triangle are 8 cm and 15 cm. How long is the longest side (in cm)?
  22. 22.The angles of a triangle are in the ratio 1 : 3 : 5. What is the biggest angle (in degrees)?
  23. 23.The two shorter sides of a right-angled triangle are 24 cm and 7 cm. How long is the longest side (in cm)?
  24. 24.In triangle ABC, angle A = 42° and angle B = 21°. What is angle C (in degrees)?
  25. 25.In an isosceles triangle, the angle between the two equal sides is 64°. What is each of the other two angles (in degrees)?
  26. 26.In an isosceles triangle, the angle between the two equal sides is 24°. What is each of the other two angles (in degrees)?
  27. 27.The two shorter sides of a right-angled triangle are 12 cm and 16 cm. How long is the longest side (in cm)?
  28. 28.In an isosceles triangle, the angle between the two equal sides is 102°. What is each of the other two angles (in degrees)?
  29. 29.An exterior angle of a triangle is 78°. One of its two interior opposite angles is 23°. What is the other one (in degrees)?
  30. 30.Can a triangle have sides of 3 cm, 7 cm and 7 cm? (a) No (b) Yes
  31. 31.In an isosceles triangle, the two equal angles are 25° each. What is the third angle (in degrees)?
  32. 32.The two interior opposite angles of a triangle are 50° and 24°. What is the exterior angle (in degrees)?
  33. 33.The two interior opposite angles of a triangle are 29° and 34°. What is the exterior angle (in degrees)?
  34. 34.The angles of a triangle are in the ratio 3 : 3 : 4. What is the biggest angle (in degrees)?
  35. 35.Can a triangle have sides of 18 cm, 10 cm and 5 cm? (a) Yes (b) No
  36. 36.In a right-angled triangle, one of the other two angles is 68°. What is the third angle (in degrees)?
  37. 37.In a right-angled triangle, one of the other two angles is 62°. What is the third angle (in degrees)?
  38. 38.In an isosceles triangle, the two equal angles are 59° each. What is the third angle (in degrees)?
  39. 39.The two interior opposite angles of a triangle are 71° and 31°. What is the exterior angle (in degrees)?
  40. 40.The angles of a triangle are in the ratio 1 : 2 : 3. What is the smallest angle (in degrees)?

Answer key

  1. 9
  2. 11
  3. 71
  4. 40
  5. 21
  6. 77
  7. 86
  8. 18
  9. 90
  10. 62
  11. 118
  12. 58
  13. 13
  14. 38
  15. 31
  16. No
  17. 12
  18. 67
  19. 24
  20. Yes
  21. 17
  22. 100
  23. 25
  24. 117
  25. 58
  26. 78
  27. 20
  28. 39
  29. 55
  30. Yes
  31. 130
  32. 74
  33. 63
  34. 72
  35. No
  36. 22
  37. 28
  38. 62
  39. 102
  40. 30

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