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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 348 · 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.An exterior angle of a triangle is 79°. One of its two interior opposite angles is 30°. What is the other one (in degrees)?
  2. 2.The angles of a triangle are in the ratio 3 : 3 : 4. What is the biggest angle (in degrees)?
  3. 3.Can a triangle have sides of 9 cm, 10 cm and 11 cm? (a) No (b) Yes
  4. 4.The two shorter sides of a right-angled triangle are 18 cm and 24 cm. How long is the longest side (in cm)?
  5. 5.The two interior opposite angles of a triangle are 21° and 25°. What is the exterior angle (in degrees)?
  6. 6.An exterior angle of a triangle is 88°. One of its two interior opposite angles is 35°. What is the other one (in degrees)?
  7. 7.An exterior angle of a triangle is 85°. One of its two interior opposite angles is 36°. What is the other one (in degrees)?
  8. 8.In triangle ABC, angle A = 46° and angle B = 24°. What is angle C (in degrees)?
  9. 9.The angles of a triangle are in the ratio 3 : 5 : 7. What is the smallest angle (in degrees)?
  10. 10.In triangle ABC, angle A = 55° and angle B = 84°. What is angle C (in degrees)?
  11. 11.The two shorter sides of a right-angled triangle are 7 cm and 24 cm. How long is the longest side (in cm)?
  12. 12.The two shorter sides of a right-angled triangle are 10 cm and 24 cm. How long is the longest side (in cm)?
  13. 13.Can a triangle have sides of 8 cm, 5 cm and 15 cm? (a) No (b) Yes
  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 an isosceles triangle, the two equal angles are 38° each. What is the third angle (in degrees)?
  16. 16.An exterior angle of a triangle is 67°. One of its two interior opposite angles is 30°. What is the other one (in degrees)?
  17. 17.The two interior opposite angles of a triangle are 30° and 34°. What is the exterior angle (in degrees)?
  18. 18.The angles of a triangle are in the ratio 2 : 3 : 4. What is the biggest angle (in degrees)?
  19. 19.In an isosceles triangle, the two equal angles are 34° each. What is the third angle (in degrees)?
  20. 20.In an isosceles triangle, the angle between the two equal sides is 56°. What is each of the other two angles (in degrees)?
  21. 21.In a right-angled triangle, one of the other two angles is 28°. What is the third angle (in degrees)?
  22. 22.In a right-angled triangle, one of the other two angles is 58°. What is the third angle (in degrees)?
  23. 23.The two shorter sides of a right-angled triangle are 3 cm and 4 cm. How long is the longest side (in cm)?
  24. 24.An exterior angle of a triangle is 49°. One of its two interior opposite angles is 22°. What is the other one (in degrees)?
  25. 25.In triangle ABC, angle A = 90° and angle B = 24°. What is angle C (in degrees)?
  26. 26.Can a triangle have sides of 8 cm, 11 cm and 8 cm? (a) No (b) Yes
  27. 27.In a right-angled triangle, one of the other two angles is 55°. What is the third angle (in degrees)?
  28. 28.In triangle ABC, angle A = 100° and angle B = 25°. What is angle C (in degrees)?
  29. 29.The angles of a triangle are in the ratio 3 : 4 : 5. What is the biggest angle (in degrees)?
  30. 30.Can a triangle have sides of 5 cm, 4 cm and 2 cm? (a) No (b) Yes
  31. 31.The two interior opposite angles of a triangle are 24° and 49°. What is the exterior angle (in degrees)?
  32. 32.In a right-angled triangle, one of the other two angles is 78°. What is the third angle (in degrees)?
  33. 33.In triangle ABC, angle A = 33° and angle B = 31°. What is angle C (in degrees)?
  34. 34.In triangle ABC, angle A = 97° and angle B = 55°. What is angle C (in degrees)?
  35. 35.The angles of a triangle are in the ratio 4 : 5 : 6. What is the smallest angle (in degrees)?
  36. 36.Can a triangle have sides of 15 cm, 6 cm and 6 cm? (a) Yes (b) No
  37. 37.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)?
  38. 38.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)?
  39. 39.The longest side of a right-angled triangle is 25 cm and one of the other sides is 15 cm. How long is the third side (in cm)?
  40. 40.In an isosceles triangle, the angle between the two equal sides is 104°. What is each of the other two angles (in degrees)?

Answer key

  1. 49
  2. 72
  3. Yes
  4. 30
  5. 46
  6. 53
  7. 49
  8. 110
  9. 36
  10. 41
  11. 25
  12. 26
  13. No
  14. 7
  15. 104
  16. 37
  17. 64
  18. 80
  19. 112
  20. 62
  21. 62
  22. 32
  23. 5
  24. 27
  25. 66
  26. Yes
  27. 35
  28. 55
  29. 75
  30. Yes
  31. 73
  32. 12
  33. 116
  34. 28
  35. 48
  36. No
  37. 15
  38. 8
  39. 20
  40. 38

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