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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 246 · 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 an isosceles triangle, the two equal angles are 69° each. What is the third angle (in degrees)?
  2. 2.In a right-angled triangle, one of the other two angles is 47°. What is the third angle (in degrees)?
  3. 3.In triangle ABC, angle A = 51° and angle B = 107°. What is angle C (in degrees)?
  4. 4.In triangle ABC, angle A = 31° and angle B = 119°. What is angle C (in degrees)?
  5. 5.The longest side of a right-angled triangle is 5 cm and one of the other sides is 4 cm. How long is the third side (in cm)?
  6. 6.The angles of a triangle are in the ratio 1 : 1 : 2. What is the smallest angle (in degrees)?
  7. 7.In triangle ABC, angle A = 77° and angle B = 48°. What is angle C (in degrees)?
  8. 8.The two shorter sides of a right-angled triangle are 8 cm and 15 cm. How long is the longest side (in cm)?
  9. 9.In a right-angled triangle, one of the other two angles is 21°. What is the third angle (in degrees)?
  10. 10.An exterior angle of a triangle is 81°. One of its two interior opposite angles is 34°. What is the other one (in degrees)?
  11. 11.The longest side of a right-angled triangle is 30 cm and one of the other sides is 18 cm. How long is the third side (in cm)?
  12. 12.In an isosceles triangle, the two equal angles are 50° each. What is the third angle (in degrees)?
  13. 13.In a right-angled triangle, one of the other two angles is 29°. What is the third angle (in degrees)?
  14. 14.In an isosceles triangle, the angle between the two equal sides is 98°. What is each of the other two angles (in degrees)?
  15. 15.In an isosceles triangle, the angle between the two equal sides is 26°. What is each of the other two angles (in degrees)?
  16. 16.In triangle ABC, angle A = 94° and angle B = 30°. What is angle C (in degrees)?
  17. 17.In a right-angled triangle, one of the other two angles is 77°. What is the third angle (in degrees)?
  18. 18.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)?
  19. 19.In an isosceles triangle, the two equal angles are 58° each. What is the third angle (in degrees)?
  20. 20.In triangle ABC, angle A = 100° and angle B = 56°. What is angle C (in degrees)?
  21. 21.In a right-angled triangle, one of the other two angles is 26°. What is the third angle (in degrees)?
  22. 22.The angles of a triangle are in the ratio 5 : 6 : 7. What is the biggest angle (in degrees)?
  23. 23.In triangle ABC, angle A = 23° and angle B = 43°. What is angle C (in degrees)?
  24. 24.Can a triangle have sides of 4 cm, 7 cm and 8 cm? (a) No (b) Yes
  25. 25.The two interior opposite angles of a triangle are 33° and 31°. What is the exterior angle (in degrees)?
  26. 26.In triangle ABC, angle A = 37° and angle B = 60°. What is angle C (in degrees)?
  27. 27.In an isosceles triangle, the two equal angles are 70° each. What is the third angle (in degrees)?
  28. 28.An exterior angle of a triangle is 70°. One of its two interior opposite angles is 43°. What is the other one (in degrees)?
  29. 29.In a right-angled triangle, one of the other two angles is 59°. What is the third angle (in degrees)?
  30. 30.The two interior opposite angles of a triangle are 47° and 63°. What is the exterior angle (in degrees)?
  31. 31.In a right-angled triangle, one of the other two angles is 31°. What is the third angle (in degrees)?
  32. 32.The two interior opposite angles of a triangle are 76° and 22°. What is the exterior angle (in degrees)?
  33. 33.The two interior opposite angles of a triangle are 51° and 35°. What is the exterior angle (in degrees)?
  34. 34.In an isosceles triangle, the two equal angles are 40° each. What is the third angle (in degrees)?
  35. 35.The two interior opposite angles of a triangle are 63° and 74°. What is the exterior angle (in degrees)?
  36. 36.The two interior opposite angles of a triangle are 65° and 30°. What is the exterior angle (in degrees)?
  37. 37.Can a triangle have sides of 7 cm, 6 cm and 16 cm? (a) No (b) Yes
  38. 38.In triangle ABC, angle A = 50° and angle B = 106°. What is angle C (in degrees)?
  39. 39.An exterior angle of a triangle is 147°. One of its two interior opposite angles is 72°. What is the other one (in degrees)?
  40. 40.In an isosceles triangle, the angle between the two equal sides is 42°. What is each of the other two angles (in degrees)?

Answer key

  1. 42
  2. 43
  3. 22
  4. 30
  5. 3
  6. 45
  7. 55
  8. 17
  9. 69
  10. 47
  11. 24
  12. 80
  13. 61
  14. 41
  15. 77
  16. 56
  17. 13
  18. 9
  19. 64
  20. 24
  21. 64
  22. 70
  23. 114
  24. Yes
  25. 64
  26. 83
  27. 40
  28. 27
  29. 31
  30. 110
  31. 59
  32. 98
  33. 86
  34. 100
  35. 137
  36. 95
  37. No
  38. 24
  39. 75
  40. 69

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