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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 760 · 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.

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  1. 1.Can a triangle have sides of 5 cm, 7 cm and 5 cm? (a) Yes (b) No
  2. 2.In a right-angled triangle, one of the other two angles is 28°. What is the third angle (in degrees)?
  3. 3.In triangle ABC, angle A = 40° and angle B = 55°. What is angle C (in degrees)?
  4. 4.The angles of a triangle are in the ratio 3 : 5 : 7. What is the smallest angle (in degrees)?
  5. 5.An exterior angle of a triangle is 131°. One of its two interior opposite angles is 57°. What is the other one (in degrees)?
  6. 6.The two shorter sides of a right-angled triangle are 24 cm and 18 cm. How long is the longest side (in cm)?
  7. 7.The two interior opposite angles of a triangle are 20° and 30°. What is the exterior angle (in degrees)?
  8. 8.In a right-angled triangle, one of the other two angles is 32°. What is the third angle (in degrees)?
  9. 9.In triangle ABC, angle A = 27° and angle B = 104°. What is angle C (in degrees)?
  10. 10.The angles of a triangle are in the ratio 2 : 7 : 9. What is the biggest angle (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.The angles of a triangle are in the ratio 1 : 2 : 3. What is the biggest angle (in degrees)?
  13. 13.Can a triangle have sides of 21 cm, 12 cm and 7 cm? (a) No (b) Yes
  14. 14.In a right-angled triangle, one of the other two angles is 57°. What is the third angle (in degrees)?
  15. 15.In a right-angled triangle, one of the other two angles is 77°. What is the third angle (in degrees)?
  16. 16.In an isosceles triangle, the angle between the two equal sides is 90°. What is each of the other two angles (in degrees)?
  17. 17.In triangle ABC, angle A = 42° and angle B = 116°. What is angle C (in degrees)?
  18. 18.In an isosceles triangle, the angle between the two equal sides is 58°. What is each of the other two angles (in degrees)?
  19. 19.The angles of a triangle are in the ratio 1 : 2 : 6. What is the biggest angle (in degrees)?
  20. 20.In a right-angled triangle, one of the other two angles is 50°. What is the third angle (in degrees)?
  21. 21.In an isosceles triangle, the two equal angles are 69° each. What is the third angle (in degrees)?
  22. 22.Can a triangle have sides of 9 cm, 6 cm and 10 cm? (a) No (b) Yes
  23. 23.In a right-angled triangle, one of the other two angles is 27°. What is the third angle (in degrees)?
  24. 24.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)?
  25. 25.In triangle ABC, angle A = 42° and angle B = 99°. What is angle C (in degrees)?
  26. 26.The two shorter sides of a right-angled triangle are 24 cm and 7 cm. How long is the longest side (in cm)?
  27. 27.Can a triangle have sides of 12 cm, 4 cm and 12 cm? (a) No (b) Yes
  28. 28.The angles of a triangle are in the ratio 4 : 5 : 6. What is the smallest angle (in degrees)?
  29. 29.Can a triangle have sides of 9 cm, 11 cm and 12 cm? (a) No (b) Yes
  30. 30.The two interior opposite angles of a triangle are 62° and 28°. What is the exterior angle (in degrees)?
  31. 31.The two interior opposite angles of a triangle are 35° and 64°. What is the exterior angle (in degrees)?
  32. 32.Can a triangle have sides of 8 cm, 9 cm and 3 cm? (a) Yes (b) No
  33. 33.In an isosceles triangle, the two equal angles are 37° each. What is the third angle (in degrees)?
  34. 34.Can a triangle have sides of 3 cm, 3 cm and 10 cm? (a) No (b) Yes
  35. 35.In a right-angled triangle, one of the other two angles is 38°. What is the third angle (in degrees)?
  36. 36.Can a triangle have sides of 10 cm, 10 cm and 3 cm? (a) No (b) Yes
  37. 37.The angles of a triangle are in the ratio 1 : 1 : 2. What is the smallest angle (in degrees)?
  38. 38.In a right-angled triangle, one of the other two angles is 56°. What is the third angle (in degrees)?
  39. 39.In a right-angled triangle, one of the other two angles is 73°. What is the third angle (in degrees)?
  40. 40.In an isosceles triangle, the angle between the two equal sides is 46°. What is each of the other two angles (in degrees)?

Answer key

  1. Yes
  2. 62
  3. 85
  4. 36
  5. 74
  6. 30
  7. 50
  8. 58
  9. 49
  10. 90
  11. 36
  12. 90
  13. No
  14. 33
  15. 13
  16. 45
  17. 22
  18. 61
  19. 120
  20. 40
  21. 42
  22. Yes
  23. 63
  24. 15
  25. 39
  26. 25
  27. Yes
  28. 48
  29. Yes
  30. 90
  31. 99
  32. Yes
  33. 106
  34. No
  35. 52
  36. Yes
  37. 45
  38. 34
  39. 17
  40. 67

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