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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 40 · 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.An exterior angle of a triangle is 115°. One of its two interior opposite angles is 61°. What is the other one (in degrees)?
  2. 2.In a right-angled triangle, one of the other two angles is 26°. What is the third angle (in degrees)?
  3. 3.The two shorter sides of a right-angled triangle are 7 cm and 24 cm. How long is the longest side (in cm)?
  4. 4.In an isosceles triangle, the angle between the two equal sides is 86°. What is each of the other two angles (in degrees)?
  5. 5.In triangle ABC, angle A = 54° and angle B = 84°. What is angle C (in degrees)?
  6. 6.In an isosceles triangle, the two equal angles are 59° each. What is the third angle (in degrees)?
  7. 7.The angles of a triangle are in the ratio 1 : 3 : 5. What is the biggest angle (in degrees)?
  8. 8.The two shorter sides of a right-angled triangle are 15 cm and 20 cm. How long is the longest side (in cm)?
  9. 9.In an isosceles triangle, the two equal angles are 63° each. What is the third angle (in degrees)?
  10. 10.In a right-angled triangle, one of the other two angles is 10°. What is the third angle (in degrees)?
  11. 11.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)?
  12. 12.In triangle ABC, angle A = 89° and angle B = 23°. What is angle C (in degrees)?
  13. 13.In triangle ABC, angle A = 26° and angle B = 88°. What is angle C (in degrees)?
  14. 14.The angles of a triangle are in the ratio 3 : 3 : 4. What is the smallest angle (in degrees)?
  15. 15.An exterior angle of a triangle is 116°. One of its two interior opposite angles is 37°. What is the other one (in degrees)?
  16. 16.The angles of a triangle are in the ratio 1 : 2 : 2. What is the smallest angle (in degrees)?
  17. 17.An exterior angle of a triangle is 119°. One of its two interior opposite angles is 48°. What is the other one (in degrees)?
  18. 18.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)?
  19. 19.The two interior opposite angles of a triangle are 40° and 71°. What is the exterior angle (in degrees)?
  20. 20.An exterior angle of a triangle is 90°. One of its two interior opposite angles is 21°. What is the other one (in degrees)?
  21. 21.The two shorter sides of a right-angled triangle are 3 cm and 4 cm. How long is the longest side (in cm)?
  22. 22.Can a triangle have sides of 8 cm, 20 cm and 7 cm? (a) Yes (b) No
  23. 23.The angles of a triangle are in the ratio 1 : 1 : 2. What is the smallest angle (in degrees)?
  24. 24.The angles of a triangle are in the ratio 3 : 5 : 7. What is the biggest angle (in degrees)?
  25. 25.In an isosceles triangle, the two equal angles are 74° each. What is the third angle (in degrees)?
  26. 26.The longest side of a right-angled triangle is 39 cm and one of the other sides is 36 cm. How long is the third side (in cm)?
  27. 27.In a right-angled triangle, one of the other two angles is 34°. What is the third angle (in degrees)?
  28. 28.In triangle ABC, angle A = 65° and angle B = 88°. What is angle C (in degrees)?
  29. 29.The angles of a triangle are in the ratio 2 : 2 : 5. What is the biggest angle (in degrees)?
  30. 30.In a right-angled triangle, one of the other two angles is 59°. What is the third angle (in degrees)?
  31. 31.Can a triangle have sides of 14 cm, 8 cm and 2 cm? (a) Yes (b) No
  32. 32.In a right-angled triangle, one of the other two angles is 44°. What is the third angle (in degrees)?
  33. 33.Can a triangle have sides of 12 cm, 4 cm and 10 cm? (a) No (b) Yes
  34. 34.The two interior opposite angles of a triangle are 61° and 76°. What is the exterior angle (in degrees)?
  35. 35.In an isosceles triangle, the two equal angles are 51° each. What is the third angle (in degrees)?
  36. 36.In an isosceles triangle, the angle between the two equal sides is 28°. What is each of the other two angles (in degrees)?
  37. 37.Can a triangle have sides of 6 cm, 5 cm and 10 cm? (a) No (b) Yes
  38. 38.In a right-angled triangle, one of the other two angles is 78°. What is the third angle (in degrees)?
  39. 39.The two interior opposite angles of a triangle are 69° and 63°. What is the exterior angle (in degrees)?
  40. 40.The angles of a triangle are in the ratio 1 : 2 : 2. What is the biggest angle (in degrees)?

Answer key

  1. 54
  2. 64
  3. 25
  4. 47
  5. 42
  6. 62
  7. 100
  8. 25
  9. 54
  10. 80
  11. 24
  12. 68
  13. 66
  14. 54
  15. 79
  16. 36
  17. 71
  18. 12
  19. 111
  20. 69
  21. 5
  22. No
  23. 45
  24. 84
  25. 32
  26. 15
  27. 56
  28. 27
  29. 100
  30. 31
  31. No
  32. 46
  33. Yes
  34. 137
  35. 78
  36. 76
  37. Yes
  38. 12
  39. 132
  40. 72

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