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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 38 · 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 12 cm, 8 cm and 6 cm? (a) No (b) Yes
  2. 2.In a right-angled triangle, one of the other two angles is 64°. What is the third angle (in degrees)?
  3. 3.The two shorter sides of a right-angled triangle are 15 cm and 20 cm. How long is the longest side (in cm)?
  4. 4.In triangle ABC, angle A = 83° and angle B = 26°. What is angle C (in degrees)?
  5. 5.In triangle ABC, angle A = 88° and angle B = 22°. What is angle C (in degrees)?
  6. 6.In an isosceles triangle, the angle between the two equal sides is 66°. What is each of the other two angles (in degrees)?
  7. 7.An exterior angle of a triangle is 77°. One of its two interior opposite angles is 39°. What is the other one (in degrees)?
  8. 8.In a right-angled triangle, one of the other two angles is 47°. What is the third angle (in degrees)?
  9. 9.The two interior opposite angles of a triangle are 23° and 77°. What is the exterior angle (in degrees)?
  10. 10.An exterior angle of a triangle is 69°. One of its two interior opposite angles is 35°. What is the other one (in degrees)?
  11. 11.In an isosceles triangle, the angle between the two equal sides is 28°. What is each of the other two angles (in degrees)?
  12. 12.Can a triangle have sides of 3 cm, 5 cm and 3 cm? (a) No (b) Yes
  13. 13.An exterior angle of a triangle is 99°. One of its two interior opposite angles is 27°. What is the other one (in degrees)?
  14. 14.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)?
  15. 15.In triangle ABC, angle A = 29° and angle B = 76°. What is angle C (in degrees)?
  16. 16.In an isosceles triangle, the two equal angles are 78° each. What is the third angle (in degrees)?
  17. 17.Can a triangle have sides of 10 cm, 2 cm and 11 cm? (a) No (b) Yes
  18. 18.In triangle ABC, angle A = 65° and angle B = 52°. What is angle C (in degrees)?
  19. 19.The angles of a triangle are in the ratio 2 : 3 : 4. What is the biggest angle (in degrees)?
  20. 20.In an isosceles triangle, the angle between the two equal sides is 60°. What is each of the other two angles (in degrees)?
  21. 21.The angles of a triangle are in the ratio 1 : 2 : 2. What is the biggest angle (in degrees)?
  22. 22.The two shorter sides of a right-angled triangle are 8 cm and 15 cm. How long is the longest side (in cm)?
  23. 23.In triangle ABC, angle A = 40° and angle B = 114°. What is angle C (in degrees)?
  24. 24.The two shorter sides of a right-angled triangle are 15 cm and 8 cm. How long is the longest side (in cm)?
  25. 25.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)?
  26. 26.In a right-angled triangle, one of the other two angles is 31°. What is the third angle (in degrees)?
  27. 27.The angles of a triangle are in the ratio 4 : 5 : 6. What is the smallest angle (in degrees)?
  28. 28.In a right-angled triangle, one of the other two angles is 71°. What is the third angle (in degrees)?
  29. 29.In an isosceles triangle, the angle between the two equal sides is 150°. What is each of the other two angles (in degrees)?
  30. 30.The two interior opposite angles of a triangle are 24° and 63°. What is the exterior angle (in degrees)?
  31. 31.In a right-angled triangle, one of the other two angles is 15°. What is the third angle (in degrees)?
  32. 32.The two interior opposite angles of a triangle are 61° and 48°. What is the exterior angle (in degrees)?
  33. 33.In an isosceles triangle, the angle between the two equal sides is 26°. What is each of the other two angles (in degrees)?
  34. 34.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)?
  35. 35.An exterior angle of a triangle is 130°. One of its two interior opposite angles is 51°. What is the other one (in degrees)?
  36. 36.In triangle ABC, angle A = 64° and angle B = 54°. What is angle C (in degrees)?
  37. 37.In triangle ABC, angle A = 69° and angle B = 28°. What is angle C (in degrees)?
  38. 38.In a right-angled triangle, one of the other two angles is 56°. What is the third angle (in degrees)?
  39. 39.The two interior opposite angles of a triangle are 73° and 53°. What is the exterior angle (in degrees)?
  40. 40.The angles of a triangle are in the ratio 3 : 3 : 4. What is the biggest angle (in degrees)?

Answer key

  1. Yes
  2. 26
  3. 25
  4. 71
  5. 70
  6. 57
  7. 38
  8. 43
  9. 100
  10. 34
  11. 76
  12. Yes
  13. 72
  14. 7
  15. 75
  16. 24
  17. Yes
  18. 63
  19. 80
  20. 60
  21. 72
  22. 17
  23. 26
  24. 17
  25. 15
  26. 59
  27. 48
  28. 19
  29. 15
  30. 87
  31. 75
  32. 109
  33. 77
  34. 8
  35. 79
  36. 62
  37. 83
  38. 34
  39. 126
  40. 72

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