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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 15 · 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 79°. What is the third angle (in degrees)?
  2. 2.The angles of a triangle are in the ratio 1 : 4 : 5. What is the biggest angle (in degrees)?
  3. 3.In triangle ABC, angle A = 24° and angle B = 51°. What is angle C (in degrees)?
  4. 4.The two interior opposite angles of a triangle are 32° and 74°. What is the exterior angle (in degrees)?
  5. 5.An exterior angle of a triangle is 86°. One of its two interior opposite angles is 37°. What is the other one (in degrees)?
  6. 6.The two shorter sides of a right-angled triangle are 15 cm and 8 cm. How long is the longest side (in cm)?
  7. 7.Can a triangle have sides of 12 cm, 8 cm and 6 cm? (a) No (b) Yes
  8. 8.In a right-angled triangle, one of the other two angles is 46°. What is the third angle (in degrees)?
  9. 9.In an isosceles triangle, the two equal angles are 49° each. What is the third angle (in degrees)?
  10. 10.The two interior opposite angles of a triangle are 26° and 78°. What is the exterior angle (in degrees)?
  11. 11.In a right-angled triangle, one of the other two angles is 53°. What is the third angle (in degrees)?
  12. 12.In triangle ABC, angle A = 51° and angle B = 20°. What is angle C (in degrees)?
  13. 13.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)?
  14. 14.The two shorter sides of a right-angled triangle are 8 cm and 15 cm. How long is the longest side (in cm)?
  15. 15.The angles of a triangle are in the ratio 3 : 4 : 5. What is the biggest angle (in degrees)?
  16. 16.Can a triangle have sides of 8 cm, 6 cm and 3 cm? (a) No (b) Yes
  17. 17.The two shorter sides of a right-angled triangle are 10 cm and 24 cm. How long is the longest side (in cm)?
  18. 18.Can a triangle have sides of 8 cm, 3 cm and 3 cm? (a) No (b) Yes
  19. 19.An exterior angle of a triangle is 88°. One of its two interior opposite angles is 49°. What is the other one (in degrees)?
  20. 20.In triangle ABC, angle A = 58° and angle B = 33°. What is angle C (in degrees)?
  21. 21.The angles of a triangle are in the ratio 1 : 1 : 2. What is the biggest angle (in degrees)?
  22. 22.The two shorter sides of a right-angled triangle are 12 cm and 5 cm. How long is the longest side (in cm)?
  23. 23.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)?
  24. 24.The angles of a triangle are in the ratio 1 : 2 : 2. What is the biggest angle (in degrees)?
  25. 25.In an isosceles triangle, the angle between the two equal sides is 84°. What is each of the other two angles (in degrees)?
  26. 26.The two interior opposite angles of a triangle are 21° and 48°. What is the exterior angle (in degrees)?
  27. 27.In a right-angled triangle, one of the other two angles is 77°. What is the third angle (in degrees)?
  28. 28.In a right-angled triangle, one of the other two angles is 28°. What is the third angle (in degrees)?
  29. 29.The angles of a triangle are in the ratio 1 : 3 : 5. What is the smallest angle (in degrees)?
  30. 30.In an isosceles triangle, the two equal angles are 68° each. What is the third angle (in degrees)?
  31. 31.In a right-angled triangle, one of the other two angles is 78°. What is the third angle (in degrees)?
  32. 32.An exterior angle of a triangle is 78°. One of its two interior opposite angles is 46°. What is the other one (in degrees)?
  33. 33.The angles of a triangle are in the ratio 1 : 2 : 6. What is the biggest angle (in degrees)?
  34. 34.An exterior angle of a triangle is 108°. One of its two interior opposite angles is 33°. What is the other one (in degrees)?
  35. 35.In an isosceles triangle, the angle between the two equal sides is 132°. What is each of the other two angles (in degrees)?
  36. 36.The longest side of a right-angled triangle is 13 cm and one of the other sides is 12 cm. How long is the third side (in cm)?
  37. 37.In an isosceles triangle, the two equal angles are 29° each. What is the third angle (in degrees)?
  38. 38.The angles of a triangle are in the ratio 2 : 3 : 5. What is the biggest angle (in degrees)?
  39. 39.Can a triangle have sides of 8 cm, 5 cm and 12 cm? (a) Yes (b) No
  40. 40.In an isosceles triangle, the two equal angles are 46° each. What is the third angle (in degrees)?

Answer key

  1. 11
  2. 90
  3. 105
  4. 106
  5. 49
  6. 17
  7. Yes
  8. 44
  9. 82
  10. 104
  11. 37
  12. 109
  13. 20
  14. 17
  15. 75
  16. Yes
  17. 26
  18. No
  19. 39
  20. 89
  21. 90
  22. 13
  23. 24
  24. 72
  25. 48
  26. 69
  27. 13
  28. 62
  29. 20
  30. 44
  31. 12
  32. 32
  33. 120
  34. 75
  35. 24
  36. 5
  37. 122
  38. 90
  39. Yes
  40. 88

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