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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 820 · 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.In an isosceles triangle, the two equal angles are 66° each. What is the third angle (in degrees)?
  2. 2.The angles of a triangle are in the ratio 2 : 2 : 5. What is the smallest angle (in degrees)?
  3. 3.Can a triangle have sides of 2 cm, 5 cm and 4 cm? (a) Yes (b) No
  4. 4.In a right-angled triangle, one of the other two angles is 59°. What is the third angle (in degrees)?
  5. 5.The two shorter sides of a right-angled triangle are 12 cm and 9 cm. How long is the longest side (in cm)?
  6. 6.The two shorter sides of a right-angled triangle are 5 cm and 12 cm. How long is the longest side (in cm)?
  7. 7.An exterior angle of a triangle is 58°. One of its two interior opposite angles is 24°. What is the other one (in degrees)?
  8. 8.In an isosceles triangle, the two equal angles are 83° each. What is the third angle (in degrees)?
  9. 9.In an isosceles triangle, the angle between the two equal sides is 94°. What is each of the other two angles (in degrees)?
  10. 10.In a right-angled triangle, one of the other two angles is 12°. What is the third angle (in degrees)?
  11. 11.In triangle ABC, angle A = 22° and angle B = 114°. What is angle C (in degrees)?
  12. 12.Can a triangle have sides of 10 cm, 18 cm and 8 cm? (a) Yes (b) No
  13. 13.An exterior angle of a triangle is 98°. One of its two interior opposite angles is 44°. What is the other one (in degrees)?
  14. 14.The angles of a triangle are in the ratio 1 : 4 : 5. What is the smallest angle (in degrees)?
  15. 15.In an isosceles triangle, the two equal angles are 67° each. What is the third angle (in degrees)?
  16. 16.Can a triangle have sides of 7 cm, 12 cm and 9 cm? (a) Yes (b) No
  17. 17.In a right-angled triangle, one of the other two angles is 24°. What is the third angle (in degrees)?
  18. 18.The longest side of a right-angled triangle is 30 cm and one of the other sides is 18 cm. How long is the third side (in cm)?
  19. 19.In an isosceles triangle, the angle between the two equal sides is 30°. What is each of the other two angles (in degrees)?
  20. 20.The two interior opposite angles of a triangle are 52° and 32°. What is the exterior angle (in degrees)?
  21. 21.Can a triangle have sides of 6 cm, 20 cm and 9 cm? (a) No (b) Yes
  22. 22.In a right-angled triangle, one of the other two angles is 49°. What is the third angle (in degrees)?
  23. 23.In triangle ABC, angle A = 65° and angle B = 83°. What is angle C (in degrees)?
  24. 24.In a right-angled triangle, one of the other two angles is 53°. What is the third angle (in degrees)?
  25. 25.The two interior opposite angles of a triangle are 21° and 73°. What is the exterior angle (in degrees)?
  26. 26.In a right-angled triangle, one of the other two angles is 71°. What is the third angle (in degrees)?
  27. 27.An exterior angle of a triangle is 90°. One of its two interior opposite angles is 52°. What is the other one (in degrees)?
  28. 28.In a right-angled triangle, one of the other two angles is 35°. What is the third angle (in degrees)?
  29. 29.The angles of a triangle are in the ratio 3 : 4 : 5. What is the smallest angle (in degrees)?
  30. 30.An exterior angle of a triangle is 68°. One of its two interior opposite angles is 31°. What is the other one (in degrees)?
  31. 31.Can a triangle have sides of 21 cm, 11 cm and 5 cm? (a) No (b) Yes
  32. 32.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)?
  33. 33.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)?
  34. 34.In triangle ABC, angle A = 86° and angle B = 34°. What is angle C (in degrees)?
  35. 35.An exterior angle of a triangle is 90°. One of its two interior opposite angles is 64°. What is the other one (in degrees)?
  36. 36.An exterior angle of a triangle is 103°. One of its two interior opposite angles is 62°. What is the other one (in degrees)?
  37. 37.In an isosceles triangle, the angle between the two equal sides is 20°. What is each of the other two angles (in degrees)?
  38. 38.The two interior opposite angles of a triangle are 27° and 27°. What is the exterior angle (in degrees)?
  39. 39.In triangle ABC, angle A = 36° and angle B = 27°. What is angle C (in degrees)?
  40. 40.The angles of a triangle are in the ratio 4 : 5 : 6. What is the biggest angle (in degrees)?

Answer key

  1. 48
  2. 40
  3. Yes
  4. 31
  5. 15
  6. 13
  7. 34
  8. 14
  9. 43
  10. 78
  11. 44
  12. No
  13. 54
  14. 18
  15. 46
  16. Yes
  17. 66
  18. 24
  19. 75
  20. 84
  21. No
  22. 41
  23. 32
  24. 37
  25. 94
  26. 19
  27. 38
  28. 55
  29. 45
  30. 37
  31. No
  32. 12
  33. 15
  34. 60
  35. 26
  36. 41
  37. 80
  38. 54
  39. 117
  40. 72

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