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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 509 · 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.

NameDateTime takenScore ___ / 40
  1. 1.Can a triangle have sides of 9 cm, 13 cm and 9 cm? (a) No (b) Yes
  2. 2.The longest side of a right-angled triangle is 10 cm and one of the other sides is 6 cm. How long is the third side (in cm)?
  3. 3.The two shorter sides of a right-angled triangle are 24 cm and 7 cm. How long is the longest side (in cm)?
  4. 4.In triangle ABC, angle A = 77° and angle B = 64°. What is angle C (in degrees)?
  5. 5.An exterior angle of a triangle is 86°. One of its two interior opposite angles is 30°. What is the other one (in degrees)?
  6. 6.An exterior angle of a triangle is 105°. One of its two interior opposite angles is 80°. What is the other one (in degrees)?
  7. 7.The two shorter sides of a right-angled triangle are 7 cm and 24 cm. How long is the longest side (in cm)?
  8. 8.An exterior angle of a triangle is 88°. One of its two interior opposite angles is 23°. What is the other one (in degrees)?
  9. 9.An exterior angle of a triangle is 97°. One of its two interior opposite angles is 38°. What is the other one (in degrees)?
  10. 10.The two interior opposite angles of a triangle are 80° and 65°. What is the exterior angle (in degrees)?
  11. 11.Can a triangle have sides of 10 cm, 20 cm and 11 cm? (a) Yes (b) No
  12. 12.Can a triangle have sides of 8 cm, 3 cm and 12 cm? (a) Yes (b) No
  13. 13.Can a triangle have sides of 11 cm, 10 cm and 13 cm? (a) No (b) Yes
  14. 14.The angles of a triangle are in the ratio 1 : 3 : 5. What is the smallest angle (in degrees)?
  15. 15.The two shorter sides of a right-angled triangle are 12 cm and 5 cm. How long is the longest side (in cm)?
  16. 16.In a right-angled triangle, one of the other two angles is 16°. What is the third angle (in degrees)?
  17. 17.The two interior opposite angles of a triangle are 20° and 35°. What is the exterior angle (in degrees)?
  18. 18.An exterior angle of a triangle is 134°. One of its two interior opposite angles is 57°. What is the other one (in degrees)?
  19. 19.In triangle ABC, angle A = 87° and angle B = 69°. What is angle C (in degrees)?
  20. 20.Can a triangle have sides of 5 cm, 3 cm and 7 cm? (a) Yes (b) No
  21. 21.In a right-angled triangle, one of the other two angles is 74°. What is the third angle (in degrees)?
  22. 22.The two interior opposite angles of a triangle are 20° and 28°. What is the exterior angle (in degrees)?
  23. 23.In a right-angled triangle, one of the other two angles is 58°. What is the third angle (in degrees)?
  24. 24.An exterior angle of a triangle is 68°. One of its two interior opposite angles is 33°. What is the other one (in degrees)?
  25. 25.In an isosceles triangle, the angle between the two equal sides is 158°. What is each of the other two angles (in degrees)?
  26. 26.In an isosceles triangle, the angle between the two equal sides is 24°. What is each of the other two angles (in degrees)?
  27. 27.An exterior angle of a triangle is 103°. One of its two interior opposite angles is 57°. What is the other one (in degrees)?
  28. 28.The angles of a triangle are in the ratio 1 : 1 : 2. What is the biggest angle (in degrees)?
  29. 29.The two interior opposite angles of a triangle are 38° and 79°. What is the exterior angle (in degrees)?
  30. 30.In an isosceles triangle, the angle between the two equal sides is 130°. What is each of the other two angles (in degrees)?
  31. 31.In an isosceles triangle, the two equal angles are 34° each. What is the third angle (in degrees)?
  32. 32.In a right-angled triangle, one of the other two angles is 69°. What is the third angle (in degrees)?
  33. 33.An exterior angle of a triangle is 86°. One of its two interior opposite angles is 24°. What is the other one (in degrees)?
  34. 34.Can a triangle have sides of 6 cm, 4 cm and 7 cm? (a) Yes (b) No
  35. 35.In triangle ABC, angle A = 84° and angle B = 24°. What is angle C (in degrees)?
  36. 36.An exterior angle of a triangle is 71°. One of its two interior opposite angles is 31°. What is the other one (in degrees)?
  37. 37.The two interior opposite angles of a triangle are 67° and 39°. What is the exterior angle (in degrees)?
  38. 38.The two interior opposite angles of a triangle are 68° and 60°. What is the exterior angle (in degrees)?
  39. 39.In triangle ABC, angle A = 81° and angle B = 72°. What is angle C (in degrees)?
  40. 40.Can a triangle have sides of 7 cm, 10 cm and 7 cm? (a) No (b) Yes

Answer key

  1. Yes
  2. 8
  3. 25
  4. 39
  5. 56
  6. 25
  7. 25
  8. 65
  9. 59
  10. 145
  11. Yes
  12. No
  13. Yes
  14. 20
  15. 13
  16. 74
  17. 55
  18. 77
  19. 24
  20. Yes
  21. 16
  22. 48
  23. 32
  24. 35
  25. 11
  26. 78
  27. 46
  28. 90
  29. 117
  30. 25
  31. 112
  32. 21
  33. 62
  34. Yes
  35. 72
  36. 40
  37. 106
  38. 128
  39. 27
  40. Yes

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