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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 654 · 40 sums
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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.

NameDateTime takenScore ___ / 40
  1. 1.In an isosceles triangle, the two equal angles are 74° each. What is the third angle (in degrees)?
  2. 2.In triangle ABC, angle A = 100° and angle B = 28°. What is angle C (in degrees)?
  3. 3.Can a triangle have sides of 20 cm, 10 cm and 9 cm? (a) Yes (b) No
  4. 4.Can a triangle have sides of 8 cm, 11 cm and 21 cm? (a) Yes (b) No
  5. 5.In a right-angled triangle, one of the other two angles is 41°. What is the third angle (in degrees)?
  6. 6.Can a triangle have sides of 4 cm, 9 cm and 10 cm? (a) No (b) Yes
  7. 7.In an isosceles triangle, the angle between the two equal sides is 124°. What is each of the other two angles (in degrees)?
  8. 8.The longest side of a right-angled triangle is 25 cm and one of the other sides is 24 cm. How long is the third side (in cm)?
  9. 9.The longest side of a right-angled triangle is 25 cm and one of the other sides is 20 cm. How long is the third side (in cm)?
  10. 10.In triangle ABC, angle A = 41° and angle B = 83°. What is angle C (in degrees)?
  11. 11.The two interior opposite angles of a triangle are 72° and 34°. What is the exterior angle (in degrees)?
  12. 12.Can a triangle have sides of 6 cm, 16 cm and 12 cm? (a) No (b) Yes
  13. 13.The angles of a triangle are in the ratio 2 : 7 : 9. What is the smallest angle (in degrees)?
  14. 14.The two interior opposite angles of a triangle are 41° and 57°. What is the exterior angle (in degrees)?
  15. 15.In a right-angled triangle, one of the other two angles is 12°. What is the third angle (in degrees)?
  16. 16.An exterior angle of a triangle is 90°. One of its two interior opposite angles is 26°. What is the other one (in degrees)?
  17. 17.The angles of a triangle are in the ratio 5 : 6 : 7. What is the smallest angle (in degrees)?
  18. 18.The two shorter sides of a right-angled triangle are 5 cm and 12 cm. How long is the longest side (in cm)?
  19. 19.The two interior opposite angles of a triangle are 69° and 67°. What is the exterior angle (in degrees)?
  20. 20.In triangle ABC, angle A = 81° and angle B = 32°. What is angle C (in degrees)?
  21. 21.Can a triangle have sides of 5 cm, 12 cm and 17 cm? (a) No (b) Yes
  22. 22.In a right-angled triangle, one of the other two angles is 55°. What is the third angle (in degrees)?
  23. 23.Can a triangle have sides of 10 cm, 9 cm and 19 cm? (a) Yes (b) No
  24. 24.In an isosceles triangle, the angle between the two equal sides is 44°. What is each of the other two angles (in degrees)?
  25. 25.Can a triangle have sides of 10 cm, 18 cm and 6 cm? (a) No (b) Yes
  26. 26.In a right-angled triangle, one of the other two angles is 33°. What is the third angle (in degrees)?
  27. 27.Can a triangle have sides of 10 cm, 26 cm and 11 cm? (a) No (b) Yes
  28. 28.In an isosceles triangle, the two equal angles are 56° each. What is the third angle (in degrees)?
  29. 29.In triangle ABC, angle A = 34° and angle B = 28°. What is angle C (in degrees)?
  30. 30.In triangle ABC, angle A = 33° and angle B = 63°. What is angle C (in degrees)?
  31. 31.The two interior opposite angles of a triangle are 42° and 23°. What is the exterior angle (in degrees)?
  32. 32.The two shorter sides of a right-angled triangle are 8 cm and 15 cm. How long is the longest side (in cm)?
  33. 33.In a right-angled triangle, one of the other two angles is 75°. What is the third angle (in degrees)?
  34. 34.The two interior opposite angles of a triangle are 70° and 51°. What is the exterior angle (in degrees)?
  35. 35.The angles of a triangle are in the ratio 2 : 2 : 5. What is the biggest angle (in degrees)?
  36. 36.In a right-angled triangle, one of the other two angles is 34°. What is the third angle (in degrees)?
  37. 37.The angles of a triangle are in the ratio 1 : 2 : 3. What is the biggest angle (in degrees)?
  38. 38.The two interior opposite angles of a triangle are 43° and 75°. What is the exterior angle (in degrees)?
  39. 39.An exterior angle of a triangle is 130°. One of its two interior opposite angles is 72°. What is the other one (in degrees)?
  40. 40.The angles of a triangle are in the ratio 3 : 4 : 5. What is the biggest angle (in degrees)?

Answer key

  1. 32
  2. 52
  3. No
  4. No
  5. 49
  6. Yes
  7. 28
  8. 7
  9. 15
  10. 56
  11. 106
  12. Yes
  13. 20
  14. 98
  15. 78
  16. 64
  17. 50
  18. 13
  19. 136
  20. 67
  21. No
  22. 35
  23. No
  24. 68
  25. No
  26. 57
  27. No
  28. 68
  29. 118
  30. 84
  31. 65
  32. 17
  33. 15
  34. 121
  35. 100
  36. 56
  37. 90
  38. 118
  39. 58
  40. 75

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