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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 469 · 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 11 cm, 9 cm and 3 cm? (a) Yes (b) No
  2. 2.In an isosceles triangle, the two equal angles are 27° each. What is the third angle (in degrees)?
  3. 3.In triangle ABC, angle A = 83° and angle B = 27°. What is angle C (in degrees)?
  4. 4.The two shorter sides of a right-angled triangle are 24 cm and 7 cm. How long is the longest side (in cm)?
  5. 5.In an isosceles triangle, the angle between the two equal sides is 142°. What is each of the other two angles (in degrees)?
  6. 6.Can a triangle have sides of 11 cm, 19 cm and 8 cm? (a) Yes (b) No
  7. 7.The angles of a triangle are in the ratio 2 : 3 : 5. What is the smallest angle (in degrees)?
  8. 8.In triangle ABC, angle A = 20° and angle B = 128°. What is angle C (in degrees)?
  9. 9.The angles of a triangle are in the ratio 1 : 2 : 3. What is the smallest angle (in degrees)?
  10. 10.In a right-angled triangle, one of the other two angles is 16°. What is the third angle (in degrees)?
  11. 11.In triangle ABC, angle A = 63° and angle B = 57°. What is angle C (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.In an isosceles triangle, the two equal angles are 29° each. What is the third angle (in degrees)?
  14. 14.In an isosceles triangle, the angle between the two equal sides is 140°. What is each of the other two angles (in degrees)?
  15. 15.In triangle ABC, angle A = 89° and angle B = 25°. What is angle C (in degrees)?
  16. 16.In a right-angled triangle, one of the other two angles is 21°. What is the third angle (in degrees)?
  17. 17.An exterior angle of a triangle is 103°. One of its two interior opposite angles is 79°. What is the other one (in degrees)?
  18. 18.An exterior angle of a triangle is 136°. One of its two interior opposite angles is 73°. What is the other one (in degrees)?
  19. 19.In a right-angled triangle, one of the other two angles is 35°. What is the third angle (in degrees)?
  20. 20.An exterior angle of a triangle is 83°. One of its two interior opposite angles is 48°. What is the other one (in degrees)?
  21. 21.The angles of a triangle are in the ratio 1 : 3 : 5. What is the smallest angle (in degrees)?
  22. 22.Can a triangle have sides of 7 cm, 7 cm and 18 cm? (a) Yes (b) No
  23. 23.In an isosceles triangle, the angle between the two equal sides is 88°. What is each of the other two angles (in degrees)?
  24. 24.In triangle ABC, angle A = 28° and angle B = 88°. What is angle C (in degrees)?
  25. 25.The two shorter sides of a right-angled triangle are 18 cm and 24 cm. How long is the longest side (in cm)?
  26. 26.Can a triangle have sides of 3 cm, 3 cm and 5 cm? (a) No (b) Yes
  27. 27.In a right-angled triangle, one of the other two angles is 44°. What is the third angle (in degrees)?
  28. 28.In a right-angled triangle, one of the other two angles is 80°. What is the third angle (in degrees)?
  29. 29.The two interior opposite angles of a triangle are 28° and 45°. What is the exterior angle (in degrees)?
  30. 30.The two interior opposite angles of a triangle are 23° and 36°. What is the exterior angle (in degrees)?
  31. 31.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)?
  32. 32.In an isosceles triangle, the angle between the two equal sides is 128°. What is each of the other two angles (in degrees)?
  33. 33.An exterior angle of a triangle is 100°. One of its two interior opposite angles is 22°. What is the other one (in degrees)?
  34. 34.The angles of a triangle are in the ratio 5 : 6 : 7. What is the smallest angle (in degrees)?
  35. 35.The two interior opposite angles of a triangle are 42° and 79°. What is the exterior angle (in degrees)?
  36. 36.In triangle ABC, angle A = 43° and angle B = 79°. What is angle C (in degrees)?
  37. 37.In an isosceles triangle, the two equal angles are 72° each. What is the third angle (in degrees)?
  38. 38.The two shorter sides of a right-angled triangle are 8 cm and 15 cm. How long is the longest side (in cm)?
  39. 39.In an isosceles triangle, the angle between the two equal sides is 110°. What is each of the other two angles (in degrees)?
  40. 40.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)?

Answer key

  1. Yes
  2. 126
  3. 70
  4. 25
  5. 19
  6. No
  7. 36
  8. 32
  9. 30
  10. 74
  11. 60
  12. 8
  13. 122
  14. 20
  15. 66
  16. 69
  17. 24
  18. 63
  19. 55
  20. 35
  21. 20
  22. No
  23. 46
  24. 64
  25. 30
  26. Yes
  27. 46
  28. 10
  29. 73
  30. 59
  31. 4
  32. 26
  33. 78
  34. 50
  35. 121
  36. 58
  37. 36
  38. 17
  39. 35
  40. 36

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