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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 853 · 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 triangle ABC, angle A = 89° and angle B = 47°. What is angle C (in degrees)?
  2. 2.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)?
  3. 3.Can a triangle have sides of 8 cm, 8 cm and 19 cm? (a) Yes (b) No
  4. 4.In triangle ABC, angle A = 48° and angle B = 111°. What is angle C (in degrees)?
  5. 5.In a right-angled triangle, one of the other two angles is 52°. What is the third angle (in degrees)?
  6. 6.The longest side of a right-angled triangle is 25 cm and one of the other sides is 15 cm. How long is the third side (in cm)?
  7. 7.In a right-angled triangle, one of the other two angles is 61°. What is the third angle (in degrees)?
  8. 8.The angles of a triangle are in the ratio 1 : 4 : 5. What is the biggest angle (in degrees)?
  9. 9.In triangle ABC, angle A = 73° and angle B = 48°. What is angle C (in degrees)?
  10. 10.The angles of a triangle are in the ratio 3 : 3 : 4. What is the biggest angle (in degrees)?
  11. 11.In an isosceles triangle, the angle between the two equal sides is 22°. What is each of the other two angles (in degrees)?
  12. 12.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)?
  13. 13.In an isosceles triangle, the angle between the two equal sides is 116°. What is each of the other two angles (in degrees)?
  14. 14.The longest side of a right-angled triangle is 20 cm and one of the other sides is 16 cm. How long is the third side (in cm)?
  15. 15.In a right-angled triangle, one of the other two angles is 19°. What is the third angle (in degrees)?
  16. 16.The two interior opposite angles of a triangle are 60° and 27°. What is the exterior angle (in degrees)?
  17. 17.In triangle ABC, angle A = 62° and angle B = 56°. What is angle C (in degrees)?
  18. 18.An exterior angle of a triangle is 133°. One of its two interior opposite angles is 65°. What is the other one (in degrees)?
  19. 19.The longest side of a right-angled triangle is 15 cm and one of the other sides is 9 cm. How long is the third side (in cm)?
  20. 20.The two interior opposite angles of a triangle are 55° and 29°. What is the exterior angle (in degrees)?
  21. 21.The angles of a triangle are in the ratio 5 : 6 : 7. What is the biggest angle (in degrees)?
  22. 22.An exterior angle of a triangle is 100°. One of its two interior opposite angles is 74°. What is the other one (in degrees)?
  23. 23.In an isosceles triangle, the two equal angles are 71° each. What is the third angle (in degrees)?
  24. 24.In a right-angled triangle, one of the other two angles is 12°. What is the third angle (in degrees)?
  25. 25.In a right-angled triangle, one of the other two angles is 76°. What is the third angle (in degrees)?
  26. 26.In triangle ABC, angle A = 95° and angle B = 27°. What is angle C (in degrees)?
  27. 27.In an isosceles triangle, the two equal angles are 33° each. What is the third angle (in degrees)?
  28. 28.The angles of a triangle are in the ratio 1 : 1 : 2. What is the smallest angle (in degrees)?
  29. 29.In triangle ABC, angle A = 43° and angle B = 77°. What is angle C (in degrees)?
  30. 30.In triangle ABC, angle A = 29° and angle B = 84°. What is angle C (in degrees)?
  31. 31.Can a triangle have sides of 20 cm, 11 cm and 6 cm? (a) Yes (b) No
  32. 32.The two shorter sides of a right-angled triangle are 9 cm and 12 cm. How long is the longest side (in cm)?
  33. 33.An exterior angle of a triangle is 112°. One of its two interior opposite angles is 60°. What is the other one (in degrees)?
  34. 34.The angles of a triangle are in the ratio 2 : 2 : 5. What is the smallest angle (in degrees)?
  35. 35.In a right-angled triangle, one of the other two angles is 53°. What is the third angle (in degrees)?
  36. 36.In a right-angled triangle, one of the other two angles is 20°. What is the third angle (in degrees)?
  37. 37.The angles of a triangle are in the ratio 1 : 3 : 5. What is the biggest angle (in degrees)?
  38. 38.An exterior angle of a triangle is 60°. One of its two interior opposite angles is 37°. What is the other one (in degrees)?
  39. 39.The two shorter sides of a right-angled triangle are 15 cm and 36 cm. How long is the longest side (in cm)?
  40. 40.An exterior angle of a triangle is 87°. One of its two interior opposite angles is 38°. What is the other one (in degrees)?

Answer key

  1. 44
  2. 6
  3. No
  4. 21
  5. 38
  6. 20
  7. 29
  8. 90
  9. 59
  10. 72
  11. 79
  12. 24
  13. 32
  14. 12
  15. 71
  16. 87
  17. 62
  18. 68
  19. 12
  20. 84
  21. 70
  22. 26
  23. 38
  24. 78
  25. 14
  26. 58
  27. 114
  28. 45
  29. 60
  30. 67
  31. No
  32. 15
  33. 52
  34. 40
  35. 37
  36. 70
  37. 100
  38. 23
  39. 39
  40. 49

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