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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 95 · 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.The angles of a triangle are in the ratio 1 : 2 : 2. What is the biggest angle (in degrees)?
  2. 2.In a right-angled triangle, one of the other two angles is 49°. What is the third angle (in degrees)?
  3. 3.The longest side of a right-angled triangle is 15 cm and one of the other sides is 12 cm. How long is the third side (in cm)?
  4. 4.In an isosceles triangle, the angle between the two equal sides is 26°. What is each of the other two angles (in degrees)?
  5. 5.In triangle ABC, angle A = 56° and angle B = 69°. What is angle C (in degrees)?
  6. 6.The angles of a triangle are in the ratio 2 : 2 : 5. What is the smallest angle (in degrees)?
  7. 7.In a right-angled triangle, one of the other two angles is 80°. What is the third angle (in degrees)?
  8. 8.Can a triangle have sides of 11 cm, 12 cm and 2 cm? (a) Yes (b) No
  9. 9.In a right-angled triangle, one of the other two angles is 15°. What is the third angle (in degrees)?
  10. 10.Can a triangle have sides of 10 cm, 12 cm and 18 cm? (a) Yes (b) No
  11. 11.In a right-angled triangle, one of the other two angles is 19°. What is the third angle (in degrees)?
  12. 12.In an isosceles triangle, the two equal angles are 53° each. What is the third angle (in degrees)?
  13. 13.The two interior opposite angles of a triangle are 49° and 78°. What is the exterior angle (in degrees)?
  14. 14.An exterior angle of a triangle is 89°. One of its two interior opposite angles is 33°. What is the other one (in degrees)?
  15. 15.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)?
  16. 16.In a right-angled triangle, one of the other two angles is 23°. What is the third angle (in degrees)?
  17. 17.In triangle ABC, angle A = 99° and angle B = 22°. What is angle C (in degrees)?
  18. 18.In a right-angled triangle, one of the other two angles is 67°. What is the third angle (in degrees)?
  19. 19.In an isosceles triangle, the two equal angles are 74° each. What is the third angle (in degrees)?
  20. 20.In triangle ABC, angle A = 72° and angle B = 55°. What is angle C (in degrees)?
  21. 21.In an isosceles triangle, the angle between the two equal sides is 38°. What is each of the other two angles (in degrees)?
  22. 22.Can a triangle have sides of 5 cm, 16 cm and 11 cm? (a) Yes (b) No
  23. 23.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)?
  24. 24.An exterior angle of a triangle is 131°. One of its two interior opposite angles is 62°. What is the other one (in degrees)?
  25. 25.The angles of a triangle are in the ratio 1 : 2 : 2. What is the smallest angle (in degrees)?
  26. 26.An exterior angle of a triangle is 96°. One of its two interior opposite angles is 73°. What is the other one (in degrees)?
  27. 27.The angles of a triangle are in the ratio 1 : 2 : 6. What is the biggest angle (in degrees)?
  28. 28.In a right-angled triangle, one of the other two angles is 64°. What is the third angle (in degrees)?
  29. 29.In an isosceles triangle, the angle between the two equal sides is 66°. What is each of the other two angles (in degrees)?
  30. 30.The angles of a triangle are in the ratio 1 : 2 : 6. What is the smallest angle (in degrees)?
  31. 31.The angles of a triangle are in the ratio 1 : 1 : 2. What is the biggest angle (in degrees)?
  32. 32.The angles of a triangle are in the ratio 3 : 4 : 5. What is the biggest angle (in degrees)?
  33. 33.In an isosceles triangle, the angle between the two equal sides is 70°. What is each of the other two angles (in degrees)?
  34. 34.The two interior opposite angles of a triangle are 71° and 47°. What is the exterior angle (in degrees)?
  35. 35.In triangle ABC, angle A = 68° and angle B = 20°. What is angle C (in degrees)?
  36. 36.In a right-angled triangle, one of the other two angles is 16°. What is the third angle (in degrees)?
  37. 37.The two interior opposite angles of a triangle are 66° and 68°. What is the exterior angle (in degrees)?
  38. 38.In an isosceles triangle, the two equal angles are 42° each. What is the third angle (in degrees)?
  39. 39.Can a triangle have sides of 20 cm, 8 cm and 7 cm? (a) Yes (b) No
  40. 40.In an isosceles triangle, the angle between the two equal sides is 80°. What is each of the other two angles (in degrees)?

Answer key

  1. 72
  2. 41
  3. 9
  4. 77
  5. 55
  6. 40
  7. 10
  8. Yes
  9. 75
  10. Yes
  11. 71
  12. 74
  13. 127
  14. 56
  15. 8
  16. 67
  17. 59
  18. 23
  19. 32
  20. 53
  21. 71
  22. No
  23. 36
  24. 69
  25. 36
  26. 23
  27. 120
  28. 26
  29. 57
  30. 20
  31. 90
  32. 75
  33. 55
  34. 118
  35. 92
  36. 74
  37. 134
  38. 96
  39. No
  40. 50

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