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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 286 · 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 angle between the two equal sides is 78°. What is each of the other two angles (in degrees)?
  2. 2.An exterior angle of a triangle is 84°. One of its two interior opposite angles is 31°. What is the other one (in degrees)?
  3. 3.The angles of a triangle are in the ratio 3 : 4 : 5. What is the smallest angle (in degrees)?
  4. 4.In triangle ABC, angle A = 35° and angle B = 89°. What is angle C (in degrees)?
  5. 5.In an isosceles triangle, the angle between the two equal sides is 30°. What is each of the other two angles (in degrees)?
  6. 6.In triangle ABC, angle A = 97° and angle B = 29°. What is angle C (in degrees)?
  7. 7.In a right-angled triangle, one of the other two angles is 40°. What is the third angle (in degrees)?
  8. 8.An exterior angle of a triangle is 121°. One of its two interior opposite angles is 59°. What is the other one (in degrees)?
  9. 9.The two shorter sides of a right-angled triangle are 7 cm and 24 cm. How long is the longest side (in cm)?
  10. 10.In triangle ABC, angle A = 23° and angle B = 61°. What is angle C (in degrees)?
  11. 11.The angles of a triangle are in the ratio 3 : 5 : 7. What is the biggest angle (in degrees)?
  12. 12.The two interior opposite angles of a triangle are 51° and 70°. What is the exterior angle (in degrees)?
  13. 13.In a right-angled triangle, one of the other two angles is 20°. What is the third angle (in degrees)?
  14. 14.In triangle ABC, angle A = 29° and angle B = 51°. What is angle C (in degrees)?
  15. 15.In an isosceles triangle, the two equal angles are 41° each. What is the third angle (in degrees)?
  16. 16.An exterior angle of a triangle is 104°. One of its two interior opposite angles is 26°. What is the other one (in degrees)?
  17. 17.In an isosceles triangle, the two equal angles are 37° each. What is the third angle (in degrees)?
  18. 18.The two shorter sides of a right-angled triangle are 15 cm and 36 cm. How long is the longest side (in cm)?
  19. 19.An exterior angle of a triangle is 91°. One of its two interior opposite angles is 55°. What is the other one (in degrees)?
  20. 20.Can a triangle have sides of 9 cm, 12 cm and 9 cm? (a) Yes (b) No
  21. 21.Can a triangle have sides of 9 cm, 10 cm and 5 cm? (a) Yes (b) No
  22. 22.Can a triangle have sides of 4 cm, 5 cm and 8 cm? (a) No (b) Yes
  23. 23.The two interior opposite angles of a triangle are 48° and 35°. What is the exterior angle (in degrees)?
  24. 24.The two shorter sides of a right-angled triangle are 12 cm and 5 cm. How long is the longest side (in cm)?
  25. 25.In triangle ABC, angle A = 39° and angle B = 28°. What is angle C (in degrees)?
  26. 26.The angles of a triangle are in the ratio 2 : 3 : 4. What is the smallest angle (in degrees)?
  27. 27.In an isosceles triangle, the angle between the two equal sides is 148°. What is each of the other two angles (in degrees)?
  28. 28.The angles of a triangle are in the ratio 5 : 6 : 7. What is the smallest angle (in degrees)?
  29. 29.The longest side of a right-angled triangle is 26 cm and one of the other sides is 24 cm. How long is the third side (in cm)?
  30. 30.The two shorter sides of a right-angled triangle are 12 cm and 9 cm. How long is the longest side (in cm)?
  31. 31.In a right-angled triangle, one of the other two angles is 11°. What is the third angle (in degrees)?
  32. 32.In an isosceles triangle, the two equal angles are 26° each. What is the third angle (in degrees)?
  33. 33.An exterior angle of a triangle is 91°. One of its two interior opposite angles is 27°. What is the other one (in degrees)?
  34. 34.In a right-angled triangle, one of the other two angles is 62°. What is the third angle (in degrees)?
  35. 35.In an isosceles triangle, the two equal angles are 45° each. What is the third angle (in degrees)?
  36. 36.In an isosceles triangle, the two equal angles are 40° each. What is the third angle (in degrees)?
  37. 37.The two interior opposite angles of a triangle are 52° and 50°. What is the exterior angle (in degrees)?
  38. 38.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)?
  39. 39.The angles of a triangle are in the ratio 2 : 3 : 5. What is the smallest angle (in degrees)?
  40. 40.In an isosceles triangle, the two equal angles are 68° each. What is the third angle (in degrees)?

Answer key

  1. 51
  2. 53
  3. 45
  4. 56
  5. 75
  6. 54
  7. 50
  8. 62
  9. 25
  10. 96
  11. 84
  12. 121
  13. 70
  14. 100
  15. 98
  16. 78
  17. 106
  18. 39
  19. 36
  20. Yes
  21. Yes
  22. Yes
  23. 83
  24. 13
  25. 113
  26. 40
  27. 16
  28. 50
  29. 10
  30. 15
  31. 79
  32. 128
  33. 64
  34. 28
  35. 90
  36. 100
  37. 102
  38. 24
  39. 36
  40. 44

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