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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 446 · 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 21 cm, 10 cm and 10 cm? (a) Yes (b) No
  2. 2.Can a triangle have sides of 13 cm, 10 cm and 12 cm? (a) Yes (b) No
  3. 3.In an isosceles triangle, the two equal angles are 46° each. What is the third angle (in degrees)?
  4. 4.The two interior opposite angles of a triangle are 76° and 23°. What is the exterior angle (in degrees)?
  5. 5.In triangle ABC, angle A = 41° and angle B = 104°. What is angle C (in degrees)?
  6. 6.In triangle ABC, angle A = 85° and angle B = 52°. What is angle C (in degrees)?
  7. 7.In an isosceles triangle, the angle between the two equal sides is 122°. What is each of the other two angles (in degrees)?
  8. 8.Can a triangle have sides of 2 cm, 14 cm and 7 cm? (a) Yes (b) No
  9. 9.The longest side of a right-angled triangle is 20 cm and one of the other sides is 12 cm. How long is the third side (in cm)?
  10. 10.In an isosceles triangle, the two equal angles are 71° each. What is the third angle (in degrees)?
  11. 11.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)?
  12. 12.An exterior angle of a triangle is 96°. One of its two interior opposite angles is 65°. What is the other one (in degrees)?
  13. 13.In a right-angled triangle, one of the other two angles is 14°. What is the third angle (in degrees)?
  14. 14.The angles of a triangle are in the ratio 1 : 2 : 6. What is the biggest angle (in degrees)?
  15. 15.In triangle ABC, angle A = 40° and angle B = 70°. What is angle C (in degrees)?
  16. 16.The angles of a triangle are in the ratio 1 : 2 : 3. What is the smallest angle (in degrees)?
  17. 17.Can a triangle have sides of 2 cm, 2 cm and 1 cm? (a) No (b) Yes
  18. 18.In a right-angled triangle, one of the other two angles is 56°. What is the third angle (in degrees)?
  19. 19.In a right-angled triangle, one of the other two angles is 75°. What is the third angle (in degrees)?
  20. 20.An exterior angle of a triangle is 96°. One of its two interior opposite angles is 70°. What is the other one (in degrees)?
  21. 21.In an isosceles triangle, the angle between the two equal sides is 48°. What is each of the other two angles (in degrees)?
  22. 22.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)?
  23. 23.In an isosceles triangle, the two equal angles are 75° each. What is the third angle (in degrees)?
  24. 24.The two interior opposite angles of a triangle are 63° and 45°. What is the exterior angle (in degrees)?
  25. 25.An exterior angle of a triangle is 71°. One of its two interior opposite angles is 35°. What is the other one (in degrees)?
  26. 26.The angles of a triangle are in the ratio 3 : 5 : 7. What is the biggest angle (in degrees)?
  27. 27.In triangle ABC, angle A = 73° and angle B = 49°. What is angle C (in degrees)?
  28. 28.In an isosceles triangle, the angle between the two equal sides is 68°. What is each of the other two angles (in degrees)?
  29. 29.In an isosceles triangle, the angle between the two equal sides is 58°. What is each of the other two angles (in degrees)?
  30. 30.In a right-angled triangle, one of the other two angles is 42°. What is the third angle (in degrees)?
  31. 31.In a right-angled triangle, one of the other two angles is 71°. What is the third angle (in degrees)?
  32. 32.In an isosceles triangle, the angle between the two equal sides is 52°. What is each of the other two angles (in degrees)?
  33. 33.The two shorter sides of a right-angled triangle are 24 cm and 7 cm. How long is the longest side (in cm)?
  34. 34.In a right-angled triangle, one of the other two angles is 44°. What is the third angle (in degrees)?
  35. 35.Can a triangle have sides of 11 cm, 23 cm and 9 cm? (a) No (b) Yes
  36. 36.In an isosceles triangle, the two equal angles are 21° each. What is the third angle (in degrees)?
  37. 37.Can a triangle have sides of 5 cm, 11 cm and 3 cm? (a) Yes (b) No
  38. 38.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)?
  39. 39.In a right-angled triangle, one of the other two angles is 15°. What is the third angle (in degrees)?
  40. 40.An exterior angle of a triangle is 72°. One of its two interior opposite angles is 21°. What is the other one (in degrees)?

Answer key

  1. No
  2. Yes
  3. 88
  4. 99
  5. 35
  6. 43
  7. 29
  8. No
  9. 16
  10. 38
  11. 7
  12. 31
  13. 76
  14. 120
  15. 70
  16. 30
  17. Yes
  18. 34
  19. 15
  20. 26
  21. 66
  22. 36
  23. 30
  24. 108
  25. 36
  26. 84
  27. 58
  28. 56
  29. 61
  30. 48
  31. 19
  32. 64
  33. 25
  34. 46
  35. No
  36. 138
  37. No
  38. 15
  39. 75
  40. 51

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