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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 367 · 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 angles of a triangle are in the ratio 3 : 4 : 5. What is the smallest angle (in degrees)?
  2. 2.In a right-angled triangle, one of the other two angles is 21°. What is the third angle (in degrees)?
  3. 3.In a right-angled triangle, one of the other two angles is 51°. What is the third angle (in degrees)?
  4. 4.The angles of a triangle are in the ratio 4 : 5 : 6. What is the smallest angle (in degrees)?
  5. 5.Can a triangle have sides of 16 cm, 3 cm and 8 cm? (a) Yes (b) No
  6. 6.Can a triangle have sides of 10 cm, 7 cm and 7 cm? (a) No (b) Yes
  7. 7.In an isosceles triangle, the two equal angles are 42° each. What is the third angle (in degrees)?
  8. 8.An exterior angle of a triangle is 140°. One of its two interior opposite angles is 67°. What is the other one (in degrees)?
  9. 9.An exterior angle of a triangle is 98°. One of its two interior opposite angles is 62°. What is the other one (in degrees)?
  10. 10.Can a triangle have sides of 6 cm, 4 cm and 12 cm? (a) Yes (b) No
  11. 11.The two interior opposite angles of a triangle are 39° and 79°. What is the exterior angle (in degrees)?
  12. 12.In a right-angled triangle, one of the other two angles is 64°. What is the third angle (in degrees)?
  13. 13.An exterior angle of a triangle is 79°. One of its two interior opposite angles is 48°. What is the other one (in degrees)?
  14. 14.The longest side of a right-angled triangle is 17 cm and one of the other sides is 15 cm. How long is the third side (in cm)?
  15. 15.In an isosceles triangle, the two equal angles are 29° each. What is the third angle (in degrees)?
  16. 16.In triangle ABC, angle A = 35° and angle B = 20°. What is angle C (in degrees)?
  17. 17.The two shorter sides of a right-angled triangle are 15 cm and 36 cm. How long is the longest side (in cm)?
  18. 18.Can a triangle have sides of 12 cm, 10 cm and 3 cm? (a) Yes (b) No
  19. 19.An exterior angle of a triangle is 89°. One of its two interior opposite angles is 67°. What is the other one (in degrees)?
  20. 20.In an isosceles triangle, the two equal angles are 32° each. What is the third angle (in degrees)?
  21. 21.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)?
  22. 22.In a right-angled triangle, one of the other two angles is 14°. What is the third angle (in degrees)?
  23. 23.In an isosceles triangle, the two equal angles are 27° each. What is the third angle (in degrees)?
  24. 24.In triangle ABC, angle A = 79° and angle B = 67°. What is angle C (in degrees)?
  25. 25.An exterior angle of a triangle is 77°. One of its two interior opposite angles is 49°. What is the other one (in degrees)?
  26. 26.The longest side of a right-angled triangle is 17 cm and one of the other sides is 8 cm. How long is the third side (in cm)?
  27. 27.An exterior angle of a triangle is 71°. One of its two interior opposite angles is 30°. What is the other one (in degrees)?
  28. 28.In triangle ABC, angle A = 84° and angle B = 28°. What is angle C (in degrees)?
  29. 29.An exterior angle of a triangle is 107°. One of its two interior opposite angles is 56°. What is the other one (in degrees)?
  30. 30.Can a triangle have sides of 11 cm, 9 cm and 23 cm? (a) No (b) Yes
  31. 31.The angles of a triangle are in the ratio 5 : 6 : 7. What is the smallest angle (in degrees)?
  32. 32.The two interior opposite angles of a triangle are 30° and 28°. What is the exterior angle (in degrees)?
  33. 33.In a right-angled triangle, one of the other two angles is 40°. What is the third angle (in degrees)?
  34. 34.In a right-angled triangle, one of the other two angles is 45°. What is the third angle (in degrees)?
  35. 35.In a right-angled triangle, one of the other two angles is 69°. What is the third angle (in degrees)?
  36. 36.Can a triangle have sides of 5 cm, 10 cm and 11 cm? (a) No (b) Yes
  37. 37.In a right-angled triangle, one of the other two angles is 67°. What is the third angle (in degrees)?
  38. 38.The longest side of a right-angled triangle is 5 cm and one of the other sides is 3 cm. How long is the third side (in cm)?
  39. 39.The angles of a triangle are in the ratio 2 : 3 : 4. What is the smallest angle (in degrees)?
  40. 40.The angles of a triangle are in the ratio 1 : 4 : 5. What is the smallest angle (in degrees)?

Answer key

  1. 45
  2. 69
  3. 39
  4. 48
  5. No
  6. Yes
  7. 96
  8. 73
  9. 36
  10. No
  11. 118
  12. 26
  13. 31
  14. 8
  15. 122
  16. 125
  17. 39
  18. Yes
  19. 22
  20. 116
  21. 5
  22. 76
  23. 126
  24. 34
  25. 28
  26. 15
  27. 41
  28. 68
  29. 51
  30. No
  31. 50
  32. 58
  33. 50
  34. 45
  35. 21
  36. Yes
  37. 23
  38. 4
  39. 40
  40. 18

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