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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 907 · 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.An exterior angle of a triangle is 100°. One of its two interior opposite angles is 30°. What is the other one (in degrees)?
  2. 2.The two interior opposite angles of a triangle are 75° and 70°. What is the exterior angle (in degrees)?
  3. 3.The angles of a triangle are in the ratio 3 : 4 : 5. What is the smallest angle (in degrees)?
  4. 4.In triangle ABC, angle A = 73° and angle B = 69°. What is angle C (in degrees)?
  5. 5.The two interior opposite angles of a triangle are 29° and 65°. What is the exterior angle (in degrees)?
  6. 6.The two interior opposite angles of a triangle are 39° and 63°. What is the exterior angle (in degrees)?
  7. 7.In triangle ABC, angle A = 68° and angle B = 73°. What is angle C (in degrees)?
  8. 8.In an isosceles triangle, the two equal angles are 20° each. What is the third angle (in degrees)?
  9. 9.An exterior angle of a triangle is 99°. One of its two interior opposite angles is 28°. What is the other one (in degrees)?
  10. 10.The angles of a triangle are in the ratio 2 : 7 : 9. What is the smallest angle (in degrees)?
  11. 11.The angles of a triangle are in the ratio 2 : 2 : 5. What is the biggest angle (in degrees)?
  12. 12.Can a triangle have sides of 10 cm, 10 cm and 4 cm? (a) Yes (b) No
  13. 13.An exterior angle of a triangle is 100°. One of its two interior opposite angles is 51°. What is the other one (in degrees)?
  14. 14.The angles of a triangle are in the ratio 1 : 4 : 5. What is the biggest angle (in degrees)?
  15. 15.In a right-angled triangle, one of the other two angles is 62°. What is the third angle (in degrees)?
  16. 16.An exterior angle of a triangle is 73°. One of its two interior opposite angles is 52°. What is the other one (in degrees)?
  17. 17.An exterior angle of a triangle is 91°. One of its two interior opposite angles is 34°. What is the other one (in degrees)?
  18. 18.In triangle ABC, angle A = 48° and angle B = 100°. What is angle C (in degrees)?
  19. 19.In an isosceles triangle, the angle between the two equal sides is 144°. What is each of the other two angles (in degrees)?
  20. 20.An exterior angle of a triangle is 69°. One of its two interior opposite angles is 20°. What is the other one (in degrees)?
  21. 21.The longest side of a right-angled triangle is 5 cm and one of the other sides is 3 cm. How long is the third side (in cm)?
  22. 22.The longest side of a right-angled triangle is 13 cm and one of the other sides is 5 cm. How long is the third side (in cm)?
  23. 23.In triangle ABC, angle A = 24° and angle B = 108°. What is angle C (in degrees)?
  24. 24.The two interior opposite angles of a triangle are 37° and 41°. What is the exterior angle (in degrees)?
  25. 25.In triangle ABC, angle A = 49° and angle B = 87°. What is angle C (in degrees)?
  26. 26.In a right-angled triangle, one of the other two angles is 21°. What is the third angle (in degrees)?
  27. 27.Can a triangle have sides of 8 cm, 13 cm and 3 cm? (a) Yes (b) No
  28. 28.In an isosceles triangle, the two equal angles are 61° each. What is the third angle (in degrees)?
  29. 29.In a right-angled triangle, one of the other two angles is 51°. What is the third angle (in degrees)?
  30. 30.Can a triangle have sides of 6 cm, 2 cm and 3 cm? (a) Yes (b) No
  31. 31.In triangle ABC, angle A = 34° and angle B = 20°. What is angle C (in degrees)?
  32. 32.Can a triangle have sides of 23 cm, 10 cm and 10 cm? (a) Yes (b) No
  33. 33.The angles of a triangle are in the ratio 1 : 2 : 6. What is the smallest angle (in degrees)?
  34. 34.An exterior angle of a triangle is 83°. One of its two interior opposite angles is 50°. What is the other one (in degrees)?
  35. 35.In an isosceles triangle, the two equal angles are 24° each. What is the third angle (in degrees)?
  36. 36.The two interior opposite angles of a triangle are 46° and 50°. What is the exterior angle (in degrees)?
  37. 37.In an isosceles triangle, the two equal angles are 67° each. What is the third angle (in degrees)?
  38. 38.An exterior angle of a triangle is 128°. One of its two interior opposite angles is 64°. What is the other one (in degrees)?
  39. 39.The two interior opposite angles of a triangle are 48° and 80°. What is the exterior angle (in degrees)?
  40. 40.The angles of a triangle are in the ratio 1 : 1 : 2. What is the smallest angle (in degrees)?

Answer key

  1. 70
  2. 145
  3. 45
  4. 38
  5. 94
  6. 102
  7. 39
  8. 140
  9. 71
  10. 20
  11. 100
  12. Yes
  13. 49
  14. 90
  15. 28
  16. 21
  17. 57
  18. 32
  19. 18
  20. 49
  21. 4
  22. 12
  23. 48
  24. 78
  25. 44
  26. 69
  27. No
  28. 58
  29. 39
  30. No
  31. 126
  32. No
  33. 20
  34. 33
  35. 132
  36. 96
  37. 46
  38. 64
  39. 128
  40. 45

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