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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 776 · 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.Can a triangle have sides of 9 cm, 9 cm and 8 cm? (a) Yes (b) No
  2. 2.In an isosceles triangle, the two equal angles are 73° each. What is the third angle (in degrees)?
  3. 3.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)?
  4. 4.Can a triangle have sides of 2 cm, 9 cm and 8 cm? (a) Yes (b) No
  5. 5.In triangle ABC, angle A = 22° and angle B = 93°. What is angle C (in degrees)?
  6. 6.The two shorter sides of a right-angled triangle are 12 cm and 16 cm. How long is the longest side (in cm)?
  7. 7.The angles of a triangle are in the ratio 2 : 3 : 5. What is the smallest angle (in degrees)?
  8. 8.In a right-angled triangle, one of the other two angles is 31°. What is the third angle (in degrees)?
  9. 9.The two shorter sides of a right-angled triangle are 15 cm and 8 cm. How long is the longest side (in cm)?
  10. 10.In triangle ABC, angle A = 85° and angle B = 35°. What is angle C (in degrees)?
  11. 11.In triangle ABC, angle A = 48° and angle B = 27°. What is angle C (in degrees)?
  12. 12.In a right-angled triangle, one of the other two angles is 10°. What is the third angle (in degrees)?
  13. 13.The angles of a triangle are in the ratio 2 : 7 : 9. What is the smallest angle (in degrees)?
  14. 14.In a right-angled triangle, one of the other two angles is 58°. What is the third angle (in degrees)?
  15. 15.In a right-angled triangle, one of the other two angles is 33°. What is the third angle (in degrees)?
  16. 16.The two interior opposite angles of a triangle are 53° and 63°. What is the exterior angle (in degrees)?
  17. 17.In a right-angled triangle, one of the other two angles is 36°. What is the third angle (in degrees)?
  18. 18.The angles of a triangle are in the ratio 4 : 5 : 6. What is the biggest angle (in degrees)?
  19. 19.In an isosceles triangle, the angle between the two equal sides is 160°. What is each of the other two angles (in degrees)?
  20. 20.In a right-angled triangle, one of the other two angles is 59°. What is the third angle (in degrees)?
  21. 21.Can a triangle have sides of 4 cm, 4 cm and 11 cm? (a) No (b) Yes
  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.The two interior opposite angles of a triangle are 50° and 25°. What is the exterior angle (in degrees)?
  24. 24.The angles of a triangle are in the ratio 2 : 2 : 5. What is the smallest angle (in degrees)?
  25. 25.In triangle ABC, angle A = 99° and angle B = 45°. What is angle C (in degrees)?
  26. 26.Can a triangle have sides of 2 cm, 2 cm and 7 cm? (a) Yes (b) No
  27. 27.In triangle ABC, angle A = 71° and angle B = 72°. What is angle C (in degrees)?
  28. 28.An exterior angle of a triangle is 146°. One of its two interior opposite angles is 74°. What is the other one (in degrees)?
  29. 29.Can a triangle have sides of 21 cm, 10 cm and 10 cm? (a) No (b) Yes
  30. 30.In an isosceles triangle, the two equal angles are 25° each. What is the third angle (in degrees)?
  31. 31.In triangle ABC, angle A = 88° and angle B = 65°. What is angle C (in degrees)?
  32. 32.Can a triangle have sides of 7 cm, 7 cm and 14 cm? (a) No (b) Yes
  33. 33.In triangle ABC, angle A = 56° and angle B = 85°. What is angle C (in degrees)?
  34. 34.In triangle ABC, angle A = 78° and angle B = 42°. What is angle C (in degrees)?
  35. 35.The angles of a triangle are in the ratio 3 : 5 : 7. What is the biggest angle (in degrees)?
  36. 36.In an isosceles triangle, the two equal angles are 21° each. What is the third angle (in degrees)?
  37. 37.In a right-angled triangle, one of the other two angles is 56°. What is the third angle (in degrees)?
  38. 38.The two interior opposite angles of a triangle are 55° and 22°. What is the exterior angle (in degrees)?
  39. 39.In a right-angled triangle, one of the other two angles is 48°. What is the third angle (in degrees)?
  40. 40.In an isosceles triangle, the angle between the two equal sides is 132°. What is each of the other two angles (in degrees)?

Answer key

  1. Yes
  2. 34
  3. 7
  4. Yes
  5. 65
  6. 20
  7. 36
  8. 59
  9. 17
  10. 60
  11. 105
  12. 80
  13. 20
  14. 32
  15. 57
  16. 116
  17. 54
  18. 72
  19. 10
  20. 31
  21. No
  22. 15
  23. 75
  24. 40
  25. 36
  26. No
  27. 37
  28. 72
  29. No
  30. 130
  31. 27
  32. No
  33. 39
  34. 60
  35. 84
  36. 138
  37. 34
  38. 77
  39. 42
  40. 24

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