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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 860 · 40 sums
TalentJR

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 two equal angles are 27° each. What is the third angle (in degrees)?
  2. 2.The two interior opposite angles of a triangle are 22° and 30°. What is the exterior angle (in degrees)?
  3. 3.In an isosceles triangle, the two equal angles are 66° each. What is the third angle (in degrees)?
  4. 4.Can a triangle have sides of 6 cm, 13 cm and 9 cm? (a) Yes (b) No
  5. 5.Can a triangle have sides of 6 cm, 6 cm and 4 cm? (a) No (b) Yes
  6. 6.The two interior opposite angles of a triangle are 79° and 24°. What is the exterior angle (in degrees)?
  7. 7.In an isosceles triangle, the angle between the two equal sides is 102°. What is each of the other two angles (in degrees)?
  8. 8.The angles of a triangle are in the ratio 1 : 4 : 5. What is the biggest angle (in degrees)?
  9. 9.In a right-angled triangle, one of the other two angles is 61°. What is the third angle (in degrees)?
  10. 10.In a right-angled triangle, one of the other two angles is 76°. What is the third angle (in degrees)?
  11. 11.The angles of a triangle are in the ratio 2 : 3 : 4. What is the biggest angle (in degrees)?
  12. 12.The two interior opposite angles of a triangle are 25° and 65°. What is the exterior angle (in degrees)?
  13. 13.In triangle ABC, angle A = 92° and angle B = 33°. What is angle C (in degrees)?
  14. 14.The two shorter sides of a right-angled triangle are 10 cm and 24 cm. How long is the longest side (in cm)?
  15. 15.In a right-angled triangle, one of the other two angles is 30°. What is the third angle (in degrees)?
  16. 16.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)?
  17. 17.Can a triangle have sides of 9 cm, 11 cm and 7 cm? (a) No (b) Yes
  18. 18.In an isosceles triangle, the angle between the two equal sides is 80°. What is each of the other two angles (in degrees)?
  19. 19.In triangle ABC, angle A = 55° and angle B = 66°. What is angle C (in degrees)?
  20. 20.The angles of a triangle are in the ratio 2 : 7 : 9. What is the smallest angle (in degrees)?
  21. 21.In a right-angled triangle, one of the other two angles is 34°. What is the third angle (in degrees)?
  22. 22.In triangle ABC, angle A = 34° and angle B = 122°. What is angle C (in degrees)?
  23. 23.In triangle ABC, angle A = 20° and angle B = 28°. What is angle C (in degrees)?
  24. 24.In triangle ABC, angle A = 97° and angle B = 38°. What is angle C (in degrees)?
  25. 25.In an isosceles triangle, the two equal angles are 34° each. What is the third angle (in degrees)?
  26. 26.In triangle ABC, angle A = 36° and angle B = 36°. What is angle C (in degrees)?
  27. 27.In triangle ABC, angle A = 65° and angle B = 78°. What is angle C (in degrees)?
  28. 28.The angles of a triangle are in the ratio 1 : 3 : 5. What is the biggest angle (in degrees)?
  29. 29.The angles of a triangle are in the ratio 1 : 1 : 2. What is the smallest angle (in degrees)?
  30. 30.An exterior angle of a triangle is 92°. One of its two interior opposite angles is 70°. What is the other one (in degrees)?
  31. 31.In an isosceles triangle, the angle between the two equal sides is 64°. What is each of the other two angles (in degrees)?
  32. 32.Can a triangle have sides of 9 cm, 9 cm and 21 cm? (a) No (b) Yes
  33. 33.The longest side of a right-angled triangle is 26 cm and one of the other sides is 24 cm. How long is the third side (in cm)?
  34. 34.The two shorter sides of a right-angled triangle are 24 cm and 18 cm. How long is the longest side (in cm)?
  35. 35.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)?
  36. 36.The two interior opposite angles of a triangle are 80° and 30°. What is the exterior angle (in degrees)?
  37. 37.The angles of a triangle are in the ratio 4 : 5 : 6. What is the smallest angle (in degrees)?
  38. 38.The angles of a triangle are in the ratio 1 : 3 : 5. What is the smallest angle (in degrees)?
  39. 39.The angles of a triangle are in the ratio 2 : 3 : 5. What is the smallest angle (in degrees)?
  40. 40.In triangle ABC, angle A = 75° and angle B = 42°. What is angle C (in degrees)?

Answer key

  1. 126
  2. 52
  3. 48
  4. Yes
  5. Yes
  6. 103
  7. 39
  8. 90
  9. 29
  10. 14
  11. 80
  12. 90
  13. 55
  14. 26
  15. 60
  16. 12
  17. Yes
  18. 50
  19. 59
  20. 20
  21. 56
  22. 24
  23. 132
  24. 45
  25. 112
  26. 108
  27. 37
  28. 100
  29. 45
  30. 22
  31. 58
  32. No
  33. 10
  34. 30
  35. 36
  36. 110
  37. 48
  38. 20
  39. 36
  40. 63

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