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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 70 · 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.The two interior opposite angles of a triangle are 21° and 23°. What is the exterior angle (in degrees)?
  2. 2.Can a triangle have sides of 8 cm, 19 cm and 7 cm? (a) No (b) Yes
  3. 3.The two shorter sides of a right-angled triangle are 3 cm and 4 cm. How long is the longest side (in cm)?
  4. 4.The angles of a triangle are in the ratio 1 : 2 : 6. What is the smallest angle (in degrees)?
  5. 5.The two shorter sides of a right-angled triangle are 15 cm and 36 cm. How long is the longest side (in cm)?
  6. 6.In a right-angled triangle, one of the other two angles is 21°. What is the third angle (in degrees)?
  7. 7.The angles of a triangle are in the ratio 1 : 2 : 2. What is the biggest angle (in degrees)?
  8. 8.In an isosceles triangle, the two equal angles are 79° each. What is the third angle (in degrees)?
  9. 9.Can a triangle have sides of 2 cm, 4 cm and 4 cm? (a) No (b) Yes
  10. 10.The angles of a triangle are in the ratio 2 : 3 : 5. What is the biggest 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 angles of a triangle are in the ratio 1 : 2 : 6. What is the biggest angle (in degrees)?
  13. 13.In triangle ABC, angle A = 82° and angle B = 53°. What is angle C (in degrees)?
  14. 14.In triangle ABC, angle A = 66° and angle B = 42°. What is angle C (in degrees)?
  15. 15.In a right-angled triangle, one of the other two angles is 78°. What is the third angle (in degrees)?
  16. 16.In triangle ABC, angle A = 48° and angle B = 109°. What is angle C (in degrees)?
  17. 17.The angles of a triangle are in the ratio 3 : 4 : 5. What is the biggest angle (in degrees)?
  18. 18.In an isosceles triangle, the two equal angles are 48° each. What is the third angle (in degrees)?
  19. 19.In triangle ABC, angle A = 36° and angle B = 96°. What is angle C (in degrees)?
  20. 20.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)?
  21. 21.Can a triangle have sides of 15 cm, 11 cm and 8 cm? (a) Yes (b) No
  22. 22.Can a triangle have sides of 11 cm, 10 cm and 8 cm? (a) Yes (b) No
  23. 23.In triangle ABC, angle A = 33° and angle B = 21°. What is angle C (in degrees)?
  24. 24.In an isosceles triangle, the angle between the two equal sides is 108°. What is each of the other two angles (in degrees)?
  25. 25.The angles of a triangle are in the ratio 1 : 2 : 3. What is the smallest 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.Can a triangle have sides of 10 cm, 3 cm and 7 cm? (a) Yes (b) No
  28. 28.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)?
  29. 29.In a right-angled triangle, one of the other two angles is 56°. What is the third angle (in degrees)?
  30. 30.The angles of a triangle are in the ratio 1 : 4 : 5. What is the biggest angle (in degrees)?
  31. 31.An exterior angle of a triangle is 87°. One of its two interior opposite angles is 58°. What is the other one (in degrees)?
  32. 32.The two interior opposite angles of a triangle are 48° and 66°. What is the exterior angle (in degrees)?
  33. 33.In triangle ABC, angle A = 46° and angle B = 30°. What is angle C (in degrees)?
  34. 34.In triangle ABC, angle A = 48° and angle B = 32°. What is angle C (in degrees)?
  35. 35.In triangle ABC, angle A = 20° and angle B = 50°. What is angle C (in degrees)?
  36. 36.In an isosceles triangle, the angle between the two equal sides is 58°. What is each of the other two angles (in degrees)?
  37. 37.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)?
  38. 38.In an isosceles triangle, the angle between the two equal sides is 110°. What is each of the other two angles (in degrees)?
  39. 39.In a right-angled triangle, one of the other two angles is 59°. What is the third angle (in degrees)?
  40. 40.In a right-angled triangle, one of the other two angles is 30°. What is the third angle (in degrees)?

Answer key

  1. 44
  2. No
  3. 5
  4. 20
  5. 39
  6. 69
  7. 72
  8. 22
  9. Yes
  10. 90
  11. 80
  12. 120
  13. 45
  14. 72
  15. 12
  16. 23
  17. 75
  18. 84
  19. 48
  20. 10
  21. Yes
  22. Yes
  23. 126
  24. 36
  25. 30
  26. 18
  27. No
  28. 7
  29. 34
  30. 90
  31. 29
  32. 114
  33. 104
  34. 100
  35. 110
  36. 61
  37. 8
  38. 35
  39. 31
  40. 60

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