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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 601 · 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.

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  1. 1.In triangle ABC, angle A = 41° and angle B = 41°. What is angle C (in degrees)?
  2. 2.In triangle ABC, angle A = 57° and angle B = 21°. What is angle C (in degrees)?
  3. 3.An exterior angle of a triangle is 91°. One of its two interior opposite angles is 30°. What is the other one (in degrees)?
  4. 4.The angles of a triangle are in the ratio 1 : 2 : 6. What is the smallest angle (in degrees)?
  5. 5.An exterior angle of a triangle is 91°. One of its two interior opposite angles is 59°. What is the other one (in degrees)?
  6. 6.In an isosceles triangle, the two equal angles are 27° each. What is the third angle (in degrees)?
  7. 7.In an isosceles triangle, the angle between the two equal sides is 78°. What is each of the other two angles (in degrees)?
  8. 8.In triangle ABC, angle A = 60° and angle B = 38°. What is angle C (in degrees)?
  9. 9.In an isosceles triangle, the two equal angles are 43° each. What is the third angle (in degrees)?
  10. 10.The two interior opposite angles of a triangle are 40° and 71°. What is the exterior angle (in degrees)?
  11. 11.In triangle ABC, angle A = 89° and angle B = 46°. What is angle C (in degrees)?
  12. 12.An exterior angle of a triangle is 110°. One of its two interior opposite angles is 74°. What is the other one (in degrees)?
  13. 13.Can a triangle have sides of 9 cm, 9 cm and 18 cm? (a) Yes (b) No
  14. 14.The two shorter sides of a right-angled triangle are 12 cm and 5 cm. How long is the longest side (in cm)?
  15. 15.Can a triangle have sides of 8 cm, 6 cm and 15 cm? (a) No (b) Yes
  16. 16.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)?
  17. 17.In triangle ABC, angle A = 20° and angle B = 80°. What is angle C (in degrees)?
  18. 18.In a right-angled triangle, one of the other two angles is 40°. What is the third angle (in degrees)?
  19. 19.The two interior opposite angles of a triangle are 31° and 78°. What is the exterior angle (in degrees)?
  20. 20.The angles of a triangle are in the ratio 4 : 5 : 6. What is the smallest angle (in degrees)?
  21. 21.In an isosceles triangle, the angle between the two equal sides is 20°. What is each of the other two angles (in degrees)?
  22. 22.In a right-angled triangle, one of the other two angles is 51°. What is the third angle (in degrees)?
  23. 23.The longest side of a right-angled triangle is 10 cm and one of the other sides is 6 cm. How long is the third side (in cm)?
  24. 24.The angles of a triangle are in the ratio 1 : 3 : 5. What is the biggest angle (in degrees)?
  25. 25.Can a triangle have sides of 7 cm, 6 cm and 11 cm? (a) No (b) Yes
  26. 26.In a right-angled triangle, one of the other two angles is 38°. What is the third angle (in degrees)?
  27. 27.The two shorter sides of a right-angled triangle are 20 cm and 15 cm. How long is the longest side (in cm)?
  28. 28.The longest side of a right-angled triangle is 10 cm and one of the other sides is 8 cm. How long is the third side (in cm)?
  29. 29.In triangle ABC, angle A = 76° and angle B = 54°. What is angle C (in degrees)?
  30. 30.In triangle ABC, angle A = 41° and angle B = 54°. What is angle C (in degrees)?
  31. 31.The angles of a triangle are in the ratio 2 : 3 : 5. What is the smallest angle (in degrees)?
  32. 32.In an isosceles triangle, the angle between the two equal sides is 120°. What is each of the other two angles (in degrees)?
  33. 33.An exterior angle of a triangle is 63°. One of its two interior opposite angles is 21°. What is the other one (in degrees)?
  34. 34.In triangle ABC, angle A = 74° and angle B = 77°. What is angle C (in degrees)?
  35. 35.In a right-angled triangle, one of the other two angles is 68°. What is the third angle (in degrees)?
  36. 36.Can a triangle have sides of 6 cm, 16 cm and 6 cm? (a) Yes (b) No
  37. 37.Can a triangle have sides of 6 cm, 4 cm and 14 cm? (a) No (b) Yes
  38. 38.An exterior angle of a triangle is 62°. One of its two interior opposite angles is 25°. What is the other one (in degrees)?
  39. 39.The angles of a triangle are in the ratio 1 : 2 : 2. What is the biggest angle (in degrees)?
  40. 40.In triangle ABC, angle A = 49° and angle B = 98°. What is angle C (in degrees)?

Answer key

  1. 98
  2. 102
  3. 61
  4. 20
  5. 32
  6. 126
  7. 51
  8. 82
  9. 94
  10. 111
  11. 45
  12. 36
  13. No
  14. 13
  15. No
  16. 8
  17. 80
  18. 50
  19. 109
  20. 48
  21. 80
  22. 39
  23. 8
  24. 100
  25. Yes
  26. 52
  27. 25
  28. 6
  29. 50
  30. 85
  31. 36
  32. 30
  33. 42
  34. 29
  35. 22
  36. No
  37. No
  38. 37
  39. 72
  40. 33

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