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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 531 · 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 two interior opposite angles of a triangle are 27° and 76°. What is the exterior angle (in degrees)?
  2. 2.The longest side of a right-angled triangle is 39 cm and one of the other sides is 36 cm. How long is the third side (in cm)?
  3. 3.In triangle ABC, angle A = 74° and angle B = 38°. What is angle C (in degrees)?
  4. 4.In an isosceles triangle, the two equal angles are 48° each. What is the third angle (in degrees)?
  5. 5.In a right-angled triangle, one of the other two angles is 40°. What is the third angle (in degrees)?
  6. 6.In a right-angled triangle, one of the other two angles is 55°. What is the third angle (in degrees)?
  7. 7.The angles of a triangle are in the ratio 1 : 2 : 3. What is the biggest angle (in degrees)?
  8. 8.In an isosceles triangle, the two equal angles are 30° each. What is the third angle (in degrees)?
  9. 9.The angles of a triangle are in the ratio 3 : 5 : 7. What is the smallest angle (in degrees)?
  10. 10.In triangle ABC, angle A = 35° and angle B = 77°. What is angle C (in degrees)?
  11. 11.In triangle ABC, angle A = 22° and angle B = 34°. What is angle C (in degrees)?
  12. 12.In a right-angled triangle, one of the other two angles is 59°. What is the third angle (in degrees)?
  13. 13.In a right-angled triangle, one of the other two angles is 20°. What is the third angle (in degrees)?
  14. 14.An exterior angle of a triangle is 81°. One of its two interior opposite angles is 59°. What is the other one (in degrees)?
  15. 15.In a right-angled triangle, one of the other two angles is 73°. What is the third angle (in degrees)?
  16. 16.In triangle ABC, angle A = 100° and angle B = 31°. What is angle C (in degrees)?
  17. 17.The two interior opposite angles of a triangle are 78° and 35°. What is the exterior angle (in degrees)?
  18. 18.In an isosceles triangle, the angle between the two equal sides is 120°. What is each of the other two angles (in degrees)?
  19. 19.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)?
  20. 20.The angles of a triangle are in the ratio 1 : 4 : 5. What is the biggest angle (in degrees)?
  21. 21.The angles of a triangle are in the ratio 1 : 2 : 3. What is the smallest angle (in degrees)?
  22. 22.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)?
  23. 23.The two shorter sides of a right-angled triangle are 15 cm and 36 cm. How long is the longest side (in cm)?
  24. 24.In triangle ABC, angle A = 29° and angle B = 62°. What is angle C (in degrees)?
  25. 25.In an isosceles triangle, the angle between the two equal sides is 152°. What is each of the other two angles (in degrees)?
  26. 26.In triangle ABC, angle A = 32° and angle B = 108°. What is angle C (in degrees)?
  27. 27.In a right-angled triangle, one of the other two angles is 17°. What is the third angle (in degrees)?
  28. 28.In an isosceles triangle, the two equal angles are 38° each. What is the third angle (in degrees)?
  29. 29.In an isosceles triangle, the two equal angles are 77° each. What is the third angle (in degrees)?
  30. 30.In a right-angled triangle, one of the other two angles is 74°. What is the third angle (in degrees)?
  31. 31.In a right-angled triangle, one of the other two angles is 76°. What is the third angle (in degrees)?
  32. 32.In an isosceles triangle, the angle between the two equal sides is 46°. What is each of the other two angles (in degrees)?
  33. 33.In an isosceles triangle, the angle between the two equal sides is 126°. What is each of the other two angles (in degrees)?
  34. 34.Can a triangle have sides of 9 cm, 14 cm and 3 cm? (a) Yes (b) No
  35. 35.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)?
  36. 36.The two interior opposite angles of a triangle are 80° and 79°. What is the exterior angle (in degrees)?
  37. 37.In an isosceles triangle, the two equal angles are 81° each. What is the third angle (in degrees)?
  38. 38.In a right-angled triangle, one of the other two angles is 56°. What is the third angle (in degrees)?
  39. 39.The angles of a triangle are in the ratio 1 : 4 : 5. What is the smallest angle (in degrees)?
  40. 40.In triangle ABC, angle A = 85° and angle B = 30°. What is angle C (in degrees)?

Answer key

  1. 103
  2. 15
  3. 68
  4. 84
  5. 50
  6. 35
  7. 90
  8. 120
  9. 36
  10. 68
  11. 124
  12. 31
  13. 70
  14. 22
  15. 17
  16. 49
  17. 113
  18. 30
  19. 7
  20. 90
  21. 30
  22. 15
  23. 39
  24. 89
  25. 14
  26. 40
  27. 73
  28. 104
  29. 26
  30. 16
  31. 14
  32. 67
  33. 27
  34. No
  35. 36
  36. 159
  37. 18
  38. 34
  39. 18
  40. 65

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