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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 395 · 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 = 69° and angle B = 53°. What is angle C (in degrees)?
  2. 2.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)?
  3. 3.The angles of a triangle are in the ratio 1 : 2 : 6. What is the biggest angle (in degrees)?
  4. 4.Can a triangle have sides of 20 cm, 10 cm and 5 cm? (a) Yes (b) No
  5. 5.In a right-angled triangle, one of the other two angles is 28°. What is the third angle (in degrees)?
  6. 6.The two shorter sides of a right-angled triangle are 5 cm and 12 cm. How long is the longest side (in cm)?
  7. 7.In an isosceles triangle, the two equal angles are 26° each. What is the third angle (in degrees)?
  8. 8.The two shorter sides of a right-angled triangle are 8 cm and 15 cm. How long is the longest side (in cm)?
  9. 9.In a right-angled triangle, one of the other two angles is 50°. What is the third angle (in degrees)?
  10. 10.In triangle ABC, angle A = 98° and angle B = 28°. What is angle C (in degrees)?
  11. 11.In an isosceles triangle, the angle between the two equal sides is 62°. What is each of the other two angles (in degrees)?
  12. 12.In an isosceles triangle, the two equal angles are 54° each. What is the third angle (in degrees)?
  13. 13.In a right-angled triangle, one of the other two angles is 15°. What is the third angle (in degrees)?
  14. 14.In triangle ABC, angle A = 24° and angle B = 78°. What is angle C (in degrees)?
  15. 15.In a right-angled triangle, one of the other two angles is 35°. What is the third angle (in degrees)?
  16. 16.The angles of a triangle are in the ratio 1 : 3 : 5. What is the biggest angle (in degrees)?
  17. 17.In triangle ABC, angle A = 21° and angle B = 56°. What is angle C (in degrees)?
  18. 18.In triangle ABC, angle A = 25° and angle B = 103°. What is angle C (in degrees)?
  19. 19.An exterior angle of a triangle is 83°. One of its two interior opposite angles is 30°. What is the other one (in degrees)?
  20. 20.An exterior angle of a triangle is 78°. One of its two interior opposite angles is 46°. What is the other one (in degrees)?
  21. 21.An exterior angle of a triangle is 56°. One of its two interior opposite angles is 25°. What is the other one (in degrees)?
  22. 22.In an isosceles triangle, the two equal angles are 23° each. What is the third angle (in degrees)?
  23. 23.In a right-angled triangle, one of the other two angles is 40°. What is the third angle (in degrees)?
  24. 24.The angles of a triangle are in the ratio 2 : 3 : 5. What is the smallest angle (in degrees)?
  25. 25.In an isosceles triangle, the two equal angles are 21° each. What is the third angle (in degrees)?
  26. 26.The two interior opposite angles of a triangle are 67° and 25°. What is the exterior angle (in degrees)?
  27. 27.Can a triangle have sides of 7 cm, 10 cm and 10 cm? (a) No (b) Yes
  28. 28.In a right-angled triangle, one of the other two angles is 65°. What is the third angle (in degrees)?
  29. 29.The angles of a triangle are in the ratio 2 : 2 : 5. What is the smallest angle (in degrees)?
  30. 30.The two interior opposite angles of a triangle are 52° and 22°. What is the exterior angle (in degrees)?
  31. 31.An exterior angle of a triangle is 122°. One of its two interior opposite angles is 69°. What is the other one (in degrees)?
  32. 32.The angles of a triangle are in the ratio 1 : 3 : 5. What is the smallest angle (in degrees)?
  33. 33.In a right-angled triangle, one of the other two angles is 14°. What is the third angle (in degrees)?
  34. 34.In triangle ABC, angle A = 21° and angle B = 95°. What is angle C (in degrees)?
  35. 35.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)?
  36. 36.In triangle ABC, angle A = 21° and angle B = 48°. What is angle C (in degrees)?
  37. 37.In a right-angled triangle, one of the other two angles is 26°. What is the third angle (in degrees)?
  38. 38.An exterior angle of a triangle is 69°. One of its two interior opposite angles is 22°. What is the other one (in degrees)?
  39. 39.In a right-angled triangle, one of the other two angles is 36°. What is the third angle (in degrees)?
  40. 40.In an isosceles triangle, the two equal angles are 79° each. What is the third angle (in degrees)?

Answer key

  1. 58
  2. 24
  3. 120
  4. No
  5. 62
  6. 13
  7. 128
  8. 17
  9. 40
  10. 54
  11. 59
  12. 72
  13. 75
  14. 78
  15. 55
  16. 100
  17. 103
  18. 52
  19. 53
  20. 32
  21. 31
  22. 134
  23. 50
  24. 36
  25. 138
  26. 92
  27. Yes
  28. 25
  29. 40
  30. 74
  31. 53
  32. 20
  33. 76
  34. 64
  35. 8
  36. 111
  37. 64
  38. 47
  39. 54
  40. 22

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