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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 844 · 40 sums
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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 a right-angled triangle, one of the other two angles is 73°. What is the third angle (in degrees)?
  2. 2.The angles of a triangle are in the ratio 1 : 4 : 5. What is the biggest angle (in degrees)?
  3. 3.The two interior opposite angles of a triangle are 24° and 22°. What is the exterior angle (in degrees)?
  4. 4.The two interior opposite angles of a triangle are 20° and 27°. What is the exterior angle (in degrees)?
  5. 5.In triangle ABC, angle A = 33° and angle B = 30°. What is angle C (in degrees)?
  6. 6.In an isosceles triangle, the two equal angles are 63° each. What is the third angle (in degrees)?
  7. 7.In a right-angled triangle, one of the other two angles is 23°. What is the third angle (in degrees)?
  8. 8.Can a triangle have sides of 12 cm, 21 cm and 7 cm? (a) Yes (b) No
  9. 9.The angles of a triangle are in the ratio 2 : 7 : 9. What is the smallest angle (in degrees)?
  10. 10.In triangle ABC, angle A = 82° and angle B = 76°. What is angle C (in degrees)?
  11. 11.The angles of a triangle are in the ratio 2 : 3 : 5. What is the smallest angle (in degrees)?
  12. 12.Can a triangle have sides of 10 cm, 19 cm and 9 cm? (a) Yes (b) No
  13. 13.Can a triangle have sides of 12 cm, 7 cm and 5 cm? (a) Yes (b) No
  14. 14.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)?
  15. 15.The angles of a triangle are in the ratio 3 : 3 : 4. What is the smallest angle (in degrees)?
  16. 16.Can a triangle have sides of 10 cm, 8 cm and 5 cm? (a) Yes (b) No
  17. 17.In a right-angled triangle, one of the other two angles is 42°. What is the third angle (in degrees)?
  18. 18.The two interior opposite angles of a triangle are 78° and 38°. What is the exterior angle (in degrees)?
  19. 19.In a right-angled triangle, one of the other two angles is 78°. What is the third angle (in degrees)?
  20. 20.In triangle ABC, angle A = 79° and angle B = 33°. What is angle C (in degrees)?
  21. 21.An exterior angle of a triangle is 125°. One of its two interior opposite angles is 51°. What is the other one (in degrees)?
  22. 22.In triangle ABC, angle A = 35° and angle B = 111°. What is angle C (in degrees)?
  23. 23.The two shorter sides of a right-angled triangle are 24 cm and 18 cm. How long is the longest side (in cm)?
  24. 24.The angles of a triangle are in the ratio 2 : 3 : 4. What is the biggest angle (in degrees)?
  25. 25.In triangle ABC, angle A = 100° and angle B = 50°. What is angle C (in degrees)?
  26. 26.In triangle ABC, angle A = 97° and angle B = 31°. What is angle C (in degrees)?
  27. 27.An exterior angle of a triangle is 107°. One of its two interior opposite angles is 35°. What is the other one (in degrees)?
  28. 28.An exterior angle of a triangle is 51°. One of its two interior opposite angles is 27°. What is the other one (in degrees)?
  29. 29.In a right-angled triangle, one of the other two angles is 38°. What is the third angle (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.In triangle ABC, angle A = 100° and angle B = 46°. What is angle C (in degrees)?
  32. 32.The angles of a triangle are in the ratio 5 : 6 : 7. What is the biggest angle (in degrees)?
  33. 33.In triangle ABC, angle A = 27° and angle B = 122°. What is angle C (in degrees)?
  34. 34.The angles of a triangle are in the ratio 2 : 3 : 5. What is the biggest angle (in degrees)?
  35. 35.In an isosceles triangle, the angle between the two equal sides is 34°. What is each of the other two angles (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.Can a triangle have sides of 7 cm, 9 cm and 2 cm? (a) Yes (b) No
  38. 38.In triangle ABC, angle A = 82° and angle B = 77°. What is angle C (in degrees)?
  39. 39.In triangle ABC, angle A = 96° and angle B = 27°. What is angle C (in degrees)?
  40. 40.The longest side of a right-angled triangle is 25 cm and one of the other sides is 7 cm. How long is the third side (in cm)?

Answer key

  1. 17
  2. 90
  3. 46
  4. 47
  5. 117
  6. 54
  7. 67
  8. No
  9. 20
  10. 22
  11. 36
  12. No
  13. No
  14. 12
  15. 54
  16. Yes
  17. 48
  18. 116
  19. 12
  20. 68
  21. 74
  22. 34
  23. 30
  24. 80
  25. 30
  26. 52
  27. 72
  28. 24
  29. 52
  30. 20
  31. 34
  32. 70
  33. 31
  34. 90
  35. 73
  36. 74
  37. No
  38. 21
  39. 57
  40. 24

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