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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 307 · 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 a right-angled triangle, one of the other two angles is 66°. What is the third angle (in degrees)?
  2. 2.The angles of a triangle are in the ratio 2 : 3 : 5. What is the biggest angle (in degrees)?
  3. 3.In an isosceles triangle, the angle between the two equal sides is 150°. What is each of the other two angles (in degrees)?
  4. 4.The two shorter sides of a right-angled triangle are 5 cm and 12 cm. How long is the longest side (in cm)?
  5. 5.In an isosceles triangle, the two equal angles are 54° each. What is the third angle (in degrees)?
  6. 6.In a right-angled triangle, one of the other two angles is 65°. What is the third angle (in degrees)?
  7. 7.In an isosceles triangle, the two equal angles are 39° each. What is the third angle (in degrees)?
  8. 8.In triangle ABC, angle A = 87° and angle B = 43°. What is angle C (in degrees)?
  9. 9.In a right-angled triangle, one of the other two angles is 21°. What is the third angle (in degrees)?
  10. 10.In triangle ABC, angle A = 45° and angle B = 84°. 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.In triangle ABC, angle A = 89° and angle B = 61°. What is angle C (in degrees)?
  13. 13.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)?
  14. 14.The two shorter sides of a right-angled triangle are 36 cm and 15 cm. How long is the longest side (in cm)?
  15. 15.The longest side of a right-angled triangle is 26 cm and one of the other sides is 10 cm. How long is the third side (in cm)?
  16. 16.In triangle ABC, angle A = 73° and angle B = 27°. What is angle C (in degrees)?
  17. 17.In triangle ABC, angle A = 38° and angle B = 65°. What is angle C (in degrees)?
  18. 18.The longest side of a right-angled triangle is 39 cm and one of the other sides is 15 cm. How long is the third side (in cm)?
  19. 19.An exterior angle of a triangle is 96°. One of its two interior opposite angles is 25°. What is the other one (in degrees)?
  20. 20.The two interior opposite angles of a triangle are 65° and 65°. What is the exterior angle (in degrees)?
  21. 21.Can a triangle have sides of 15 cm, 7 cm and 7 cm? (a) Yes (b) No
  22. 22.In triangle ABC, angle A = 38° and angle B = 97°. What is angle C (in degrees)?
  23. 23.An exterior angle of a triangle is 128°. One of its two interior opposite angles is 64°. What is the other one (in degrees)?
  24. 24.In a right-angled triangle, one of the other two angles is 15°. What is the third angle (in degrees)?
  25. 25.The angles of a triangle are in the ratio 2 : 2 : 5. What is the biggest angle (in degrees)?
  26. 26.An exterior angle of a triangle is 115°. One of its two interior opposite angles is 64°. What is the other one (in degrees)?
  27. 27.An exterior angle of a triangle is 48°. One of its two interior opposite angles is 26°. What is the other one (in degrees)?
  28. 28.In an isosceles triangle, the angle between the two equal sides is 22°. What is each of the other two angles (in degrees)?
  29. 29.The two shorter sides of a right-angled triangle are 12 cm and 16 cm. How long is the longest side (in cm)?
  30. 30.In an isosceles triangle, the two equal angles are 76° each. What is the third angle (in degrees)?
  31. 31.The angles of a triangle are in the ratio 1 : 2 : 2. What is the biggest angle (in degrees)?
  32. 32.Can a triangle have sides of 7 cm, 17 cm and 7 cm? (a) No (b) Yes
  33. 33.Can a triangle have sides of 7 cm, 4 cm and 7 cm? (a) No (b) Yes
  34. 34.Can a triangle have sides of 11 cm, 20 cm and 8 cm? (a) Yes (b) No
  35. 35.The two shorter sides of a right-angled triangle are 15 cm and 20 cm. How long is the longest side (in cm)?
  36. 36.The two interior opposite angles of a triangle are 23° and 26°. What is the exterior angle (in degrees)?
  37. 37.In triangle ABC, angle A = 46° and angle B = 74°. What is angle C (in degrees)?
  38. 38.In triangle ABC, angle A = 26° and angle B = 63°. What is angle C (in degrees)?
  39. 39.In an isosceles triangle, the angle between the two equal sides is 52°. What is each of the other two angles (in degrees)?
  40. 40.In a right-angled triangle, one of the other two angles is 32°. What is the third angle (in degrees)?

Answer key

  1. 24
  2. 90
  3. 15
  4. 13
  5. 72
  6. 25
  7. 102
  8. 50
  9. 69
  10. 51
  11. 36
  12. 30
  13. 24
  14. 39
  15. 24
  16. 80
  17. 77
  18. 36
  19. 71
  20. 130
  21. No
  22. 45
  23. 64
  24. 75
  25. 100
  26. 51
  27. 22
  28. 79
  29. 20
  30. 28
  31. 72
  32. No
  33. Yes
  34. No
  35. 25
  36. 49
  37. 60
  38. 91
  39. 64
  40. 58

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