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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 880 · 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 = 25° and angle B = 45°. What is angle C (in degrees)?
  2. 2.An exterior angle of a triangle is 53°. One of its two interior opposite angles is 30°. What is the other one (in degrees)?
  3. 3.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)?
  4. 4.The two shorter sides of a right-angled triangle are 15 cm and 8 cm. How long is the longest side (in cm)?
  5. 5.The two shorter sides of a right-angled triangle are 10 cm and 24 cm. How long is the longest side (in cm)?
  6. 6.In an isosceles triangle, the two equal angles are 78° each. What is the third angle (in degrees)?
  7. 7.In a right-angled triangle, one of the other two angles is 76°. What is the third angle (in degrees)?
  8. 8.Can a triangle have sides of 8 cm, 8 cm and 13 cm? (a) No (b) Yes
  9. 9.In triangle ABC, angle A = 36° and angle B = 74°. What is angle C (in degrees)?
  10. 10.Can a triangle have sides of 9 cm, 7 cm and 8 cm? (a) No (b) Yes
  11. 11.The angles of a triangle are in the ratio 1 : 3 : 5. What is the smallest angle (in degrees)?
  12. 12.In an isosceles triangle, the two equal angles are 28° each. What is the third angle (in degrees)?
  13. 13.In triangle ABC, angle A = 67° and angle B = 29°. What is angle C (in degrees)?
  14. 14.In a right-angled triangle, one of the other two angles is 11°. What is the third angle (in degrees)?
  15. 15.In triangle ABC, angle A = 95° and angle B = 39°. What is angle C (in degrees)?
  16. 16.In an isosceles triangle, the angle between the two equal sides is 144°. What is each of the other two angles (in degrees)?
  17. 17.In triangle ABC, angle A = 66° and angle B = 75°. What is angle C (in degrees)?
  18. 18.In an isosceles triangle, the two equal angles are 61° each. What is the third angle (in degrees)?
  19. 19.In a right-angled triangle, one of the other two angles is 38°. What is the third angle (in degrees)?
  20. 20.In a right-angled triangle, one of the other two angles is 80°. What is the third angle (in degrees)?
  21. 21.In a right-angled triangle, one of the other two angles is 53°. What is the third angle (in degrees)?
  22. 22.In triangle ABC, angle A = 22° and angle B = 123°. What is angle C (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.Can a triangle have sides of 8 cm, 11 cm and 8 cm? (a) Yes (b) No
  25. 25.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)?
  26. 26.The two shorter sides of a right-angled triangle are 12 cm and 5 cm. How long is the longest side (in cm)?
  27. 27.The angles of a triangle are in the ratio 1 : 4 : 5. What is the smallest angle (in degrees)?
  28. 28.An exterior angle of a triangle is 121°. One of its two interior opposite angles is 51°. What is the other one (in degrees)?
  29. 29.The two shorter sides of a right-angled triangle are 24 cm and 7 cm. How long is the longest side (in cm)?
  30. 30.In a right-angled triangle, one of the other two angles is 51°. What is the third angle (in degrees)?
  31. 31.In an isosceles triangle, the two equal angles are 77° each. What is the third angle (in degrees)?
  32. 32.Can a triangle have sides of 5 cm, 12 cm and 5 cm? (a) Yes (b) No
  33. 33.In triangle ABC, angle A = 72° and angle B = 46°. What is angle C (in degrees)?
  34. 34.The two shorter sides of a right-angled triangle are 7 cm and 24 cm. How long is the longest side (in cm)?
  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.The angles of a triangle are in the ratio 3 : 5 : 7. What is the smallest angle (in degrees)?
  37. 37.In triangle ABC, angle A = 22° and angle B = 38°. What is angle C (in degrees)?
  38. 38.In triangle ABC, angle A = 90° and angle B = 35°. What is angle C (in degrees)?
  39. 39.An exterior angle of a triangle is 111°. One of its two interior opposite angles is 78°. What is the other one (in degrees)?
  40. 40.In a right-angled triangle, one of the other two angles is 75°. What is the third angle (in degrees)?

Answer key

  1. 110
  2. 23
  3. 15
  4. 17
  5. 26
  6. 24
  7. 14
  8. Yes
  9. 70
  10. Yes
  11. 20
  12. 124
  13. 84
  14. 79
  15. 46
  16. 18
  17. 39
  18. 58
  19. 52
  20. 10
  21. 37
  22. 35
  23. 17
  24. Yes
  25. 4
  26. 13
  27. 18
  28. 70
  29. 25
  30. 39
  31. 26
  32. No
  33. 62
  34. 25
  35. 8
  36. 36
  37. 120
  38. 55
  39. 33
  40. 15

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