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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 780 · 40 sums
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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 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)?
  2. 2.In a right-angled triangle, one of the other two angles is 69°. What is the third angle (in degrees)?
  3. 3.The two interior opposite angles of a triangle are 25° and 50°. What is the exterior angle (in degrees)?
  4. 4.Can a triangle have sides of 16 cm, 10 cm and 9 cm? (a) No (b) Yes
  5. 5.In an isosceles triangle, the angle between the two equal sides is 56°. What is each of the other two angles (in degrees)?
  6. 6.The angles of a triangle are in the ratio 1 : 3 : 5. What is the smallest angle (in degrees)?
  7. 7.The two interior opposite angles of a triangle are 58° and 68°. What is the exterior angle (in degrees)?
  8. 8.In triangle ABC, angle A = 60° and angle B = 95°. What is angle C (in degrees)?
  9. 9.Can a triangle have sides of 8 cm, 9 cm and 8 cm? (a) No (b) Yes
  10. 10.In a right-angled triangle, one of the other two angles is 54°. What is the third 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 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)?
  13. 13.The two interior opposite angles of a triangle are 26° and 65°. What is the exterior angle (in degrees)?
  14. 14.In triangle ABC, angle A = 56° and angle B = 39°. What is angle C (in degrees)?
  15. 15.Can a triangle have sides of 8 cm, 14 cm and 8 cm? (a) Yes (b) No
  16. 16.In an isosceles triangle, the two equal angles are 47° each. What is the third angle (in degrees)?
  17. 17.The angles of a triangle are in the ratio 4 : 5 : 6. What is the biggest angle (in degrees)?
  18. 18.Can a triangle have sides of 9 cm, 14 cm and 9 cm? (a) No (b) Yes
  19. 19.In a right-angled triangle, one of the other two angles is 75°. What is the third angle (in degrees)?
  20. 20.In an isosceles triangle, the two equal angles are 71° each. What is the third angle (in degrees)?
  21. 21.In an isosceles triangle, the two equal angles are 23° each. What is the third angle (in degrees)?
  22. 22.In an isosceles triangle, the two equal angles are 63° each. What is the third angle (in degrees)?
  23. 23.Can a triangle have sides of 10 cm, 11 cm and 10 cm? (a) No (b) Yes
  24. 24.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)?
  25. 25.In an isosceles triangle, the two equal angles are 65° each. What is the third angle (in degrees)?
  26. 26.In an isosceles triangle, the two equal angles are 27° each. What is the third angle (in degrees)?
  27. 27.Can a triangle have sides of 10 cm, 12 cm and 4 cm? (a) Yes (b) No
  28. 28.The two shorter sides of a right-angled triangle are 8 cm and 15 cm. How long is the longest side (in cm)?
  29. 29.In a right-angled triangle, one of the other two angles is 63°. What is the third angle (in degrees)?
  30. 30.Can a triangle have sides of 5 cm, 4 cm and 10 cm? (a) No (b) Yes
  31. 31.In a right-angled triangle, one of the other two angles is 13°. What is the third angle (in degrees)?
  32. 32.In triangle ABC, angle A = 56° and angle B = 34°. What is angle C (in degrees)?
  33. 33.The two interior opposite angles of a triangle are 46° and 45°. What is the exterior angle (in degrees)?
  34. 34.In a right-angled triangle, one of the other two angles is 74°. What is the third angle (in degrees)?
  35. 35.The angles of a triangle are in the ratio 1 : 2 : 3. What is the smallest angle (in degrees)?
  36. 36.The angles of a triangle are in the ratio 2 : 2 : 5. What is the biggest angle (in degrees)?
  37. 37.In a right-angled triangle, one of the other two angles is 27°. What is the third angle (in degrees)?
  38. 38.Can a triangle have sides of 12 cm, 5 cm and 9 cm? (a) No (b) Yes
  39. 39.In a right-angled triangle, one of the other two angles is 26°. What is the third angle (in degrees)?
  40. 40.In triangle ABC, angle A = 79° and angle B = 58°. What is angle C (in degrees)?

Answer key

  1. 7
  2. 21
  3. 75
  4. Yes
  5. 62
  6. 20
  7. 126
  8. 25
  9. Yes
  10. 36
  11. 45
  12. 8
  13. 91
  14. 85
  15. Yes
  16. 86
  17. 72
  18. Yes
  19. 15
  20. 38
  21. 134
  22. 54
  23. Yes
  24. 24
  25. 50
  26. 126
  27. Yes
  28. 17
  29. 27
  30. No
  31. 77
  32. 90
  33. 91
  34. 16
  35. 30
  36. 100
  37. 63
  38. Yes
  39. 64
  40. 43

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