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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 790 · 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.In a right-angled triangle, one of the other two angles is 73°. What is the third angle (in degrees)?
  2. 2.In an isosceles triangle, the two equal angles are 20° each. What is the third angle (in degrees)?
  3. 3.In triangle ABC, angle A = 92° and angle B = 39°. What is angle C (in degrees)?
  4. 4.In a right-angled triangle, one of the other two angles is 43°. What is the third angle (in degrees)?
  5. 5.In an isosceles triangle, the two equal angles are 36° each. What is the third angle (in degrees)?
  6. 6.The longest side of a right-angled triangle is 25 cm and one of the other sides is 15 cm. How long is the third side (in cm)?
  7. 7.In a right-angled triangle, one of the other two angles is 74°. What is the third angle (in degrees)?
  8. 8.In an isosceles triangle, the two equal angles are 83° each. What is the third angle (in degrees)?
  9. 9.In an isosceles triangle, the angle between the two equal sides is 74°. What is each of the other two angles (in degrees)?
  10. 10.The two interior opposite angles of a triangle are 35° and 67°. What is the exterior angle (in degrees)?
  11. 11.In a right-angled triangle, one of the other two angles is 20°. What is the third angle (in degrees)?
  12. 12.In an isosceles triangle, the angle between the two equal sides is 48°. What is each of the other two angles (in degrees)?
  13. 13.In a right-angled triangle, one of the other two angles is 10°. What is the third angle (in degrees)?
  14. 14.An exterior angle of a triangle is 79°. One of its two interior opposite angles is 24°. What is the other one (in degrees)?
  15. 15.The angles of a triangle are in the ratio 5 : 6 : 7. What is the biggest angle (in degrees)?
  16. 16.In an isosceles triangle, the angle between the two equal sides is 108°. What is each of the other two angles (in degrees)?
  17. 17.Can a triangle have sides of 9 cm, 7 cm and 17 cm? (a) No (b) Yes
  18. 18.The angles of a triangle are in the ratio 1 : 4 : 5. What is the biggest angle (in degrees)?
  19. 19.In a right-angled triangle, one of the other two angles is 48°. What is the third angle (in degrees)?
  20. 20.The angles of a triangle are in the ratio 2 : 3 : 5. What is the biggest angle (in degrees)?
  21. 21.The longest side of a right-angled triangle is 26 cm and one of the other sides is 10 cm. How long is the third side (in cm)?
  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.Can a triangle have sides of 10 cm, 10 cm and 23 cm? (a) Yes (b) No
  24. 24.In a right-angled triangle, one of the other two angles is 13°. What is the third angle (in degrees)?
  25. 25.In an isosceles triangle, the two equal angles are 35° each. What is the third angle (in degrees)?
  26. 26.Can a triangle have sides of 5 cm, 7 cm and 11 cm? (a) No (b) Yes
  27. 27.The angles of a triangle are in the ratio 1 : 1 : 2. What is the biggest angle (in degrees)?
  28. 28.Can a triangle have sides of 10 cm, 11 cm and 21 cm? (a) No (b) Yes
  29. 29.In a right-angled triangle, one of the other two angles is 51°. What is the third angle (in degrees)?
  30. 30.In a right-angled triangle, one of the other two angles is 27°. What is the third angle (in degrees)?
  31. 31.The two shorter sides of a right-angled triangle are 7 cm and 24 cm. How long is the longest side (in cm)?
  32. 32.The two shorter sides of a right-angled triangle are 15 cm and 36 cm. How long is the longest side (in cm)?
  33. 33.In an isosceles triangle, the angle between the two equal sides is 76°. What is each of the other two angles (in degrees)?
  34. 34.An exterior angle of a triangle is 103°. One of its two interior opposite angles is 27°. What is the other one (in degrees)?
  35. 35.The longest side of a right-angled triangle is 30 cm and one of the other sides is 24 cm. How long is the third side (in cm)?
  36. 36.The two interior opposite angles of a triangle are 74° and 73°. What is the exterior angle (in degrees)?
  37. 37.In an isosceles triangle, the two equal angles are 64° each. What is the third angle (in degrees)?
  38. 38.In triangle ABC, angle A = 47° and angle B = 92°. What is angle C (in degrees)?
  39. 39.In a right-angled triangle, one of the other two angles is 22°. What is the third angle (in degrees)?
  40. 40.The two interior opposite angles of a triangle are 35° and 31°. What is the exterior angle (in degrees)?

Answer key

  1. 17
  2. 140
  3. 49
  4. 47
  5. 108
  6. 20
  7. 16
  8. 14
  9. 53
  10. 102
  11. 70
  12. 66
  13. 80
  14. 55
  15. 70
  16. 36
  17. No
  18. 90
  19. 42
  20. 90
  21. 24
  22. 15
  23. No
  24. 77
  25. 110
  26. Yes
  27. 90
  28. No
  29. 39
  30. 63
  31. 25
  32. 39
  33. 52
  34. 76
  35. 18
  36. 147
  37. 52
  38. 41
  39. 68
  40. 66

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