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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 955 · 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 a right-angled triangle, one of the other two angles is 34°. What is the third angle (in degrees)?
  2. 2.In triangle ABC, angle A = 45° and angle B = 96°. What is angle C (in degrees)?
  3. 3.In an isosceles triangle, the two equal angles are 59° each. What is the third angle (in degrees)?
  4. 4.In a right-angled triangle, one of the other two angles is 57°. What is the third angle (in degrees)?
  5. 5.The angles of a triangle are in the ratio 4 : 5 : 6. What is the biggest angle (in degrees)?
  6. 6.The two interior opposite angles of a triangle are 28° and 30°. What is the exterior angle (in degrees)?
  7. 7.The two shorter sides of a right-angled triangle are 20 cm and 15 cm. How long is the longest side (in cm)?
  8. 8.In a right-angled triangle, one of the other two angles is 20°. What is the third angle (in degrees)?
  9. 9.In triangle ABC, angle A = 60° and angle B = 94°. What is angle C (in degrees)?
  10. 10.The longest side of a right-angled triangle is 30 cm and one of the other sides is 18 cm. How long is the third side (in cm)?
  11. 11.In an isosceles triangle, the two equal angles are 81° each. What is the third angle (in degrees)?
  12. 12.In a right-angled triangle, one of the other two angles is 74°. What is the third angle (in degrees)?
  13. 13.In a right-angled triangle, one of the other two angles is 51°. What is the third angle (in degrees)?
  14. 14.An exterior angle of a triangle is 104°. One of its two interior opposite angles is 63°. What is the other one (in degrees)?
  15. 15.In triangle ABC, angle A = 85° and angle B = 44°. What is angle C (in degrees)?
  16. 16.The two shorter sides of a right-angled triangle are 15 cm and 20 cm. How long is the longest side (in cm)?
  17. 17.The two interior opposite angles of a triangle are 36° and 69°. What is the exterior angle (in degrees)?
  18. 18.In triangle ABC, angle A = 69° and angle B = 26°. What is angle C (in degrees)?
  19. 19.In a right-angled triangle, one of the other two angles is 56°. What is the third angle (in degrees)?
  20. 20.The angles of a triangle are in the ratio 1 : 4 : 5. What is the smallest angle (in degrees)?
  21. 21.Can a triangle have sides of 3 cm, 7 cm and 3 cm? (a) No (b) Yes
  22. 22.The two interior opposite angles of a triangle are 73° and 31°. What is the exterior angle (in degrees)?
  23. 23.The two shorter sides of a right-angled triangle are 8 cm and 15 cm. How long is the longest side (in cm)?
  24. 24.In an isosceles triangle, the angle between the two equal sides is 102°. What is each of the other two angles (in degrees)?
  25. 25.The angles of a triangle are in the ratio 3 : 4 : 5. What is the biggest angle (in degrees)?
  26. 26.The two interior opposite angles of a triangle are 67° and 23°. What is the exterior angle (in degrees)?
  27. 27.In triangle ABC, angle A = 29° and angle B = 23°. What is angle C (in degrees)?
  28. 28.In a right-angled triangle, one of the other two angles is 76°. What is the third angle (in degrees)?
  29. 29.Can a triangle have sides of 9 cm, 19 cm and 8 cm? (a) No (b) Yes
  30. 30.An exterior angle of a triangle is 54°. One of its two interior opposite angles is 28°. What is the other one (in degrees)?
  31. 31.In an isosceles triangle, the two equal angles are 56° each. What is the third angle (in degrees)?
  32. 32.In triangle ABC, angle A = 62° and angle B = 68°. What is angle C (in degrees)?
  33. 33.In triangle ABC, angle A = 97° and angle B = 28°. What is angle C (in degrees)?
  34. 34.In an isosceles triangle, the angle between the two equal sides is 116°. What is each of the other two angles (in degrees)?
  35. 35.In a right-angled triangle, one of the other two angles is 18°. What is the third angle (in degrees)?
  36. 36.In an isosceles triangle, the angle between the two equal sides is 132°. What is each of the other two angles (in degrees)?
  37. 37.In triangle ABC, angle A = 22° and angle B = 111°. What is angle C (in degrees)?
  38. 38.In a right-angled triangle, one of the other two angles is 16°. What is the third angle (in degrees)?
  39. 39.In a right-angled triangle, one of the other two angles is 37°. What is the third angle (in degrees)?
  40. 40.In a right-angled triangle, one of the other two angles is 33°. What is the third angle (in degrees)?

Answer key

  1. 56
  2. 39
  3. 62
  4. 33
  5. 72
  6. 58
  7. 25
  8. 70
  9. 26
  10. 24
  11. 18
  12. 16
  13. 39
  14. 41
  15. 51
  16. 25
  17. 105
  18. 85
  19. 34
  20. 18
  21. No
  22. 104
  23. 17
  24. 39
  25. 75
  26. 90
  27. 128
  28. 14
  29. No
  30. 26
  31. 68
  32. 50
  33. 55
  34. 32
  35. 72
  36. 24
  37. 47
  38. 74
  39. 53
  40. 57

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