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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 76 · 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 = 49° and angle B = 86°. What is angle C (in degrees)?
  2. 2.In an isosceles triangle, the two equal angles are 69° each. What is the third angle (in degrees)?
  3. 3.An exterior angle of a triangle is 72°. One of its two interior opposite angles is 30°. What is the other one (in degrees)?
  4. 4.In an isosceles triangle, the two equal angles are 54° each. What is the third angle (in degrees)?
  5. 5.The two interior opposite angles of a triangle are 51° and 21°. What is the exterior angle (in degrees)?
  6. 6.The angles of a triangle are in the ratio 1 : 4 : 5. What is the biggest angle (in degrees)?
  7. 7.In triangle ABC, angle A = 56° and angle B = 37°. What is angle C (in degrees)?
  8. 8.Can a triangle have sides of 6 cm, 4 cm and 7 cm? (a) Yes (b) No
  9. 9.The angles of a triangle are in the ratio 2 : 7 : 9. What is the biggest angle (in degrees)?
  10. 10.The angles of a triangle are in the ratio 5 : 6 : 7. What is the biggest angle (in degrees)?
  11. 11.In a right-angled triangle, one of the other two angles is 45°. What is the third angle (in degrees)?
  12. 12.The two interior opposite angles of a triangle are 33° and 38°. What is the exterior angle (in degrees)?
  13. 13.The longest side of a right-angled triangle is 5 cm and one of the other sides is 3 cm. How long is the third side (in cm)?
  14. 14.The longest side of a right-angled triangle is 17 cm and one of the other sides is 15 cm. How long is the third side (in cm)?
  15. 15.Can a triangle have sides of 6 cm, 8 cm and 14 cm? (a) No (b) Yes
  16. 16.An exterior angle of a triangle is 80°. One of its two interior opposite angles is 59°. What is the other one (in degrees)?
  17. 17.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)?
  18. 18.In a right-angled triangle, one of the other two angles is 26°. What is the third angle (in degrees)?
  19. 19.The angles of a triangle are in the ratio 3 : 5 : 7. What is the biggest angle (in degrees)?
  20. 20.In a right-angled triangle, one of the other two angles is 18°. What is the third angle (in degrees)?
  21. 21.In triangle ABC, angle A = 82° and angle B = 73°. What is angle C (in degrees)?
  22. 22.In an isosceles triangle, the angle between the two equal sides is 106°. What is each of the other two angles (in degrees)?
  23. 23.The angles of a triangle are in the ratio 2 : 7 : 9. What is the smallest angle (in degrees)?
  24. 24.The angles of a triangle are in the ratio 2 : 3 : 5. What is the biggest angle (in degrees)?
  25. 25.Can a triangle have sides of 10 cm, 25 cm and 10 cm? (a) Yes (b) No
  26. 26.The angles of a triangle are in the ratio 4 : 5 : 6. What is the biggest angle (in degrees)?
  27. 27.Can a triangle have sides of 8 cm, 17 cm and 6 cm? (a) Yes (b) No
  28. 28.The two shorter sides of a right-angled triangle are 36 cm and 15 cm. How long is the longest side (in cm)?
  29. 29.The angles of a triangle are in the ratio 2 : 3 : 4. What is the biggest angle (in degrees)?
  30. 30.The two shorter sides of a right-angled triangle are 15 cm and 8 cm. How long is the longest side (in cm)?
  31. 31.In triangle ABC, angle A = 48° and angle B = 48°. What is angle C (in degrees)?
  32. 32.In an isosceles triangle, the angle between the two equal sides is 124°. What is each of the other two angles (in degrees)?
  33. 33.In an isosceles triangle, the angle between the two equal sides is 102°. What is each of the other two angles (in degrees)?
  34. 34.The two interior opposite angles of a triangle are 55° and 43°. What is the exterior angle (in degrees)?
  35. 35.The longest side of a right-angled triangle is 13 cm and one of the other sides is 12 cm. How long is the third side (in cm)?
  36. 36.In an isosceles triangle, the angle between the two equal sides is 94°. What is each of the other two angles (in degrees)?
  37. 37.In triangle ABC, angle A = 27° and angle B = 121°. What is angle C (in degrees)?
  38. 38.In a right-angled triangle, one of the other two angles is 55°. What is the third angle (in degrees)?
  39. 39.The longest side of a right-angled triangle is 26 cm and one of the other sides is 24 cm. How long is the third side (in cm)?
  40. 40.An exterior angle of a triangle is 76°. One of its two interior opposite angles is 29°. What is the other one (in degrees)?

Answer key

  1. 45
  2. 42
  3. 42
  4. 72
  5. 72
  6. 90
  7. 87
  8. Yes
  9. 90
  10. 70
  11. 45
  12. 71
  13. 4
  14. 8
  15. No
  16. 21
  17. 36
  18. 64
  19. 84
  20. 72
  21. 25
  22. 37
  23. 20
  24. 90
  25. No
  26. 72
  27. No
  28. 39
  29. 80
  30. 17
  31. 84
  32. 28
  33. 39
  34. 98
  35. 5
  36. 43
  37. 32
  38. 35
  39. 10
  40. 47

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