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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 733 · 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.In an isosceles triangle, the angle between the two equal sides is 40°. What is each of the other two angles (in degrees)?
  2. 2.The two shorter sides of a right-angled triangle are 24 cm and 7 cm. How long is the longest side (in cm)?
  3. 3.Can a triangle have sides of 4 cm, 4 cm and 7 cm? (a) No (b) Yes
  4. 4.In a right-angled triangle, one of the other two angles is 66°. What is the third angle (in degrees)?
  5. 5.In an isosceles triangle, the two equal angles are 64° each. What is the third angle (in degrees)?
  6. 6.The angles of a triangle are in the ratio 1 : 2 : 2. What is the biggest angle (in degrees)?
  7. 7.In a right-angled triangle, one of the other two angles is 60°. What is the third angle (in degrees)?
  8. 8.The two shorter sides of a right-angled triangle are 12 cm and 9 cm. How long is the longest side (in cm)?
  9. 9.The two interior opposite angles of a triangle are 34° and 48°. What is the exterior angle (in degrees)?
  10. 10.In a right-angled triangle, one of the other two angles is 61°. What is the third angle (in degrees)?
  11. 11.In an isosceles triangle, the two equal angles are 76° each. What is the third angle (in degrees)?
  12. 12.In triangle ABC, angle A = 34° and angle B = 31°. What is angle C (in degrees)?
  13. 13.In an isosceles triangle, the two equal angles are 85° each. What is the third angle (in degrees)?
  14. 14.In an isosceles triangle, the two equal angles are 83° each. What is the third angle (in degrees)?
  15. 15.The angles of a triangle are in the ratio 3 : 5 : 7. What is the biggest angle (in degrees)?
  16. 16.In triangle ABC, angle A = 37° and angle B = 79°. What is angle C (in degrees)?
  17. 17.The angles of a triangle are in the ratio 1 : 1 : 2. What is the biggest angle (in degrees)?
  18. 18.In triangle ABC, angle A = 77° and angle B = 44°. What is angle C (in degrees)?
  19. 19.In an isosceles triangle, the angle between the two equal sides is 112°. What is each of the other two angles (in degrees)?
  20. 20.The two interior opposite angles of a triangle are 65° and 60°. What is the exterior angle (in degrees)?
  21. 21.In an isosceles triangle, the two equal angles are 75° each. What is the third angle (in degrees)?
  22. 22.In triangle ABC, angle A = 71° and angle B = 26°. What is angle C (in degrees)?
  23. 23.In an isosceles triangle, the angle between the two equal sides is 94°. What is each of the other two angles (in degrees)?
  24. 24.In a right-angled triangle, one of the other two angles is 22°. What is the third angle (in degrees)?
  25. 25.The angles of a triangle are in the ratio 2 : 7 : 9. What is the biggest angle (in degrees)?
  26. 26.The angles of a triangle are in the ratio 1 : 4 : 5. What is the smallest angle (in degrees)?
  27. 27.In an isosceles triangle, the two equal angles are 32° each. What is the third angle (in degrees)?
  28. 28.Can a triangle have sides of 7 cm, 12 cm and 21 cm? (a) No (b) Yes
  29. 29.The longest side of a right-angled triangle is 15 cm and one of the other sides is 9 cm. How long is the third side (in cm)?
  30. 30.The angles of a triangle are in the ratio 1 : 2 : 6. What is the biggest angle (in degrees)?
  31. 31.In triangle ABC, angle A = 26° and angle B = 111°. What is angle C (in degrees)?
  32. 32.Can a triangle have sides of 11 cm, 9 cm and 9 cm? (a) Yes (b) No
  33. 33.In an isosceles triangle, the two equal angles are 58° each. What is the third angle (in degrees)?
  34. 34.In triangle ABC, angle A = 90° and angle B = 34°. What is angle C (in degrees)?
  35. 35.In a right-angled triangle, one of the other two angles is 29°. What is the third angle (in degrees)?
  36. 36.In triangle ABC, angle A = 93° and angle B = 49°. What is angle C (in degrees)?
  37. 37.The angles of a triangle are in the ratio 2 : 2 : 5. What is the biggest angle (in degrees)?
  38. 38.In triangle ABC, angle A = 55° and angle B = 34°. What is angle C (in degrees)?
  39. 39.In an isosceles triangle, the angle between the two equal sides is 118°. What is each of the other two angles (in degrees)?
  40. 40.The angles of a triangle are in the ratio 4 : 5 : 6. What is the smallest angle (in degrees)?

Answer key

  1. 70
  2. 25
  3. Yes
  4. 24
  5. 52
  6. 72
  7. 30
  8. 15
  9. 82
  10. 29
  11. 28
  12. 115
  13. 10
  14. 14
  15. 84
  16. 64
  17. 90
  18. 59
  19. 34
  20. 125
  21. 30
  22. 83
  23. 43
  24. 68
  25. 90
  26. 18
  27. 116
  28. No
  29. 12
  30. 120
  31. 43
  32. Yes
  33. 64
  34. 56
  35. 61
  36. 38
  37. 100
  38. 91
  39. 31
  40. 48

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