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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 160 · 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 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)?
  2. 2.In an isosceles triangle, the angle between the two equal sides is 136°. What is each of the other two angles (in degrees)?
  3. 3.In triangle ABC, angle A = 78° and angle B = 35°. What is angle C (in degrees)?
  4. 4.In a right-angled triangle, one of the other two angles is 48°. What is the third angle (in degrees)?
  5. 5.In an isosceles triangle, the angle between the two equal sides is 92°. What is each of the other two angles (in degrees)?
  6. 6.An exterior angle of a triangle is 98°. One of its two interior opposite angles is 70°. What is the other one (in degrees)?
  7. 7.In an isosceles triangle, the two equal angles are 53° each. What is the third angle (in degrees)?
  8. 8.In a right-angled triangle, one of the other two angles is 55°. What is the third angle (in degrees)?
  9. 9.In an isosceles triangle, the angle between the two equal sides is 52°. What is each of the other two angles (in degrees)?
  10. 10.An exterior angle of a triangle is 147°. One of its two interior opposite angles is 79°. What is the other one (in degrees)?
  11. 11.In triangle ABC, angle A = 24° and angle B = 48°. What is angle C (in degrees)?
  12. 12.In triangle ABC, angle A = 26° and angle B = 87°. What is angle C (in degrees)?
  13. 13.The two interior opposite angles of a triangle are 50° and 27°. What is the exterior angle (in degrees)?
  14. 14.In a right-angled triangle, one of the other two angles is 32°. What is the third angle (in degrees)?
  15. 15.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)?
  16. 16.In a right-angled triangle, one of the other two angles is 20°. What is the third angle (in degrees)?
  17. 17.In an isosceles triangle, the two equal angles are 47° each. What is the third angle (in degrees)?
  18. 18.In triangle ABC, angle A = 51° and angle B = 60°. What is angle C (in degrees)?
  19. 19.In triangle ABC, angle A = 68° and angle B = 46°. What is angle C (in degrees)?
  20. 20.In a right-angled triangle, one of the other two angles is 73°. What is the third angle (in degrees)?
  21. 21.In an isosceles triangle, the two equal angles are 44° each. What is the third angle (in degrees)?
  22. 22.Can a triangle have sides of 8 cm, 18 cm and 8 cm? (a) No (b) Yes
  23. 23.Can a triangle have sides of 6 cm, 11 cm and 17 cm? (a) Yes (b) No
  24. 24.In triangle ABC, angle A = 36° and angle B = 79°. What is angle C (in degrees)?
  25. 25.Can a triangle have sides of 10 cm, 10 cm and 2 cm? (a) No (b) Yes
  26. 26.In a right-angled triangle, one of the other two angles is 57°. What is the third angle (in degrees)?
  27. 27.The angles of a triangle are in the ratio 1 : 2 : 2. What is the smallest angle (in degrees)?
  28. 28.In a right-angled triangle, one of the other two angles is 63°. What is the third angle (in degrees)?
  29. 29.The two interior opposite angles of a triangle are 59° and 20°. What is the exterior angle (in degrees)?
  30. 30.In triangle ABC, angle A = 67° and angle B = 35°. What is angle C (in degrees)?
  31. 31.In an isosceles triangle, the two equal angles are 74° each. What is the third angle (in degrees)?
  32. 32.The angles of a triangle are in the ratio 1 : 2 : 3. What is the biggest angle (in degrees)?
  33. 33.In triangle ABC, angle A = 75° and angle B = 78°. What is angle C (in degrees)?
  34. 34.The two shorter sides of a right-angled triangle are 5 cm and 12 cm. How long is the longest side (in cm)?
  35. 35.The angles of a triangle are in the ratio 1 : 3 : 5. What is the biggest angle (in degrees)?
  36. 36.In triangle ABC, angle A = 55° and angle B = 56°. What is angle C (in degrees)?
  37. 37.The two interior opposite angles of a triangle are 20° and 59°. What is the exterior angle (in degrees)?
  38. 38.An exterior angle of a triangle is 89°. One of its two interior opposite angles is 46°. What is the other one (in degrees)?
  39. 39.In triangle ABC, angle A = 58° and angle B = 30°. What is angle C (in degrees)?
  40. 40.In an isosceles triangle, the angle between the two equal sides is 68°. What is each of the other two angles (in degrees)?

Answer key

  1. 20
  2. 22
  3. 67
  4. 42
  5. 44
  6. 28
  7. 74
  8. 35
  9. 64
  10. 68
  11. 108
  12. 67
  13. 77
  14. 58
  15. 12
  16. 70
  17. 86
  18. 69
  19. 66
  20. 17
  21. 92
  22. No
  23. No
  24. 65
  25. Yes
  26. 33
  27. 36
  28. 27
  29. 79
  30. 78
  31. 32
  32. 90
  33. 27
  34. 13
  35. 100
  36. 69
  37. 79
  38. 43
  39. 92
  40. 56

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