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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 661 · 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 47°. What is the third angle (in degrees)?
  2. 2.In triangle ABC, angle A = 91° and angle B = 40°. What is angle C (in degrees)?
  3. 3.In triangle ABC, angle A = 65° and angle B = 40°. What is angle C (in degrees)?
  4. 4.The angles of a triangle are in the ratio 1 : 2 : 3. What is the smallest angle (in degrees)?
  5. 5.In an isosceles triangle, the angle between the two equal sides is 26°. What is each of the other two angles (in degrees)?
  6. 6.In triangle ABC, angle A = 59° and angle B = 56°. What is angle C (in degrees)?
  7. 7.Can a triangle have sides of 12 cm, 7 cm and 21 cm? (a) Yes (b) No
  8. 8.In triangle ABC, angle A = 59° and angle B = 29°. What is angle C (in degrees)?
  9. 9.In an isosceles triangle, the angle between the two equal sides is 84°. What is each of the other two angles (in degrees)?
  10. 10.Can a triangle have sides of 4 cm, 11 cm and 2 cm? (a) No (b) Yes
  11. 11.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)?
  12. 12.In an isosceles triangle, the angle between the two equal sides is 38°. What is each of the other two angles (in degrees)?
  13. 13.Can a triangle have sides of 11 cm, 21 cm and 5 cm? (a) No (b) Yes
  14. 14.An exterior angle of a triangle is 60°. One of its two interior opposite angles is 26°. 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.An exterior angle of a triangle is 104°. One of its two interior opposite angles is 42°. What is the other one (in degrees)?
  17. 17.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)?
  18. 18.Can a triangle have sides of 4 cm, 6 cm and 4 cm? (a) Yes (b) No
  19. 19.The two interior opposite angles of a triangle are 70° and 39°. What is the exterior angle (in degrees)?
  20. 20.In triangle ABC, angle A = 88° and angle B = 43°. What is angle C (in degrees)?
  21. 21.In a right-angled triangle, one of the other two angles is 41°. What is the third angle (in degrees)?
  22. 22.In a right-angled triangle, one of the other two angles is 21°. What is the third angle (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.In an isosceles triangle, the angle between the two equal sides is 22°. What is each of the other two angles (in degrees)?
  25. 25.The two shorter sides of a right-angled triangle are 3 cm and 4 cm. How long is the longest side (in cm)?
  26. 26.The two interior opposite angles of a triangle are 61° and 58°. What is the exterior angle (in degrees)?
  27. 27.In an isosceles triangle, the two equal angles are 21° each. What is the third angle (in degrees)?
  28. 28.An exterior angle of a triangle is 139°. One of its two interior opposite angles is 73°. What is the other one (in degrees)?
  29. 29.The angles of a triangle are in the ratio 1 : 2 : 6. What is the biggest angle (in degrees)?
  30. 30.In an isosceles triangle, the two equal angles are 77° each. What is the third angle (in degrees)?
  31. 31.In a right-angled triangle, one of the other two angles is 38°. What is the third angle (in degrees)?
  32. 32.An exterior angle of a triangle is 59°. One of its two interior opposite angles is 23°. What is the other one (in degrees)?
  33. 33.In triangle ABC, angle A = 69° and angle B = 65°. What is angle C (in degrees)?
  34. 34.In a right-angled triangle, one of the other two angles is 70°. What is the third angle (in degrees)?
  35. 35.In triangle ABC, angle A = 42° and angle B = 107°. What is angle C (in degrees)?
  36. 36.The angles of a triangle are in the ratio 2 : 3 : 4. What is the biggest angle (in degrees)?
  37. 37.In an isosceles triangle, the angle between the two equal sides is 122°. What is each of the other two angles (in degrees)?
  38. 38.In an isosceles triangle, the angle between the two equal sides is 72°. What is each of the other two angles (in degrees)?
  39. 39.The longest side of a right-angled triangle is 20 cm and one of the other sides is 16 cm. How long is the third side (in cm)?
  40. 40.Can a triangle have sides of 6 cm, 13 cm and 5 cm? (a) Yes (b) No

Answer key

  1. 43
  2. 49
  3. 75
  4. 30
  5. 77
  6. 65
  7. No
  8. 92
  9. 48
  10. No
  11. 36
  12. 71
  13. No
  14. 34
  15. 70
  16. 62
  17. 15
  18. Yes
  19. 109
  20. 49
  21. 49
  22. 69
  23. 17
  24. 79
  25. 5
  26. 119
  27. 138
  28. 66
  29. 120
  30. 26
  31. 52
  32. 36
  33. 46
  34. 20
  35. 31
  36. 80
  37. 29
  38. 54
  39. 12
  40. No

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