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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 947 · 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 an isosceles triangle, the two equal angles are 21° each. What is the third angle (in degrees)?
  2. 2.The angles of a triangle are in the ratio 2 : 3 : 4. What is the smallest angle (in degrees)?
  3. 3.An exterior angle of a triangle is 51°. One of its two interior opposite angles is 20°. What is the other one (in degrees)?
  4. 4.In an isosceles triangle, the angle between the two equal sides is 138°. What is each of the other two angles (in degrees)?
  5. 5.The angles of a triangle are in the ratio 1 : 4 : 5. What is the biggest angle (in degrees)?
  6. 6.The angles of a triangle are in the ratio 1 : 2 : 3. What is the biggest angle (in degrees)?
  7. 7.In triangle ABC, angle A = 47° and angle B = 67°. What is angle C (in degrees)?
  8. 8.The angles of a triangle are in the ratio 2 : 3 : 4. What is the biggest angle (in degrees)?
  9. 9.In triangle ABC, angle A = 27° and angle B = 58°. What is angle C (in degrees)?
  10. 10.The angles of a triangle are in the ratio 3 : 4 : 5. What is the smallest angle (in degrees)?
  11. 11.The angles of a triangle are in the ratio 2 : 2 : 5. What is the biggest angle (in degrees)?
  12. 12.In a right-angled triangle, one of the other two angles is 46°. What is the third angle (in degrees)?
  13. 13.In triangle ABC, angle A = 90° and angle B = 25°. What is angle C (in degrees)?
  14. 14.In triangle ABC, angle A = 39° and angle B = 51°. What is angle C (in degrees)?
  15. 15.Can a triangle have sides of 19 cm, 11 cm and 7 cm? (a) No (b) Yes
  16. 16.An exterior angle of a triangle is 74°. One of its two interior opposite angles is 31°. What is the other one (in degrees)?
  17. 17.In an isosceles triangle, the two equal angles are 26° each. What is the third angle (in degrees)?
  18. 18.In an isosceles triangle, the angle between the two equal sides is 56°. What is each of the other two angles (in degrees)?
  19. 19.Can a triangle have sides of 12 cm, 11 cm and 3 cm? (a) No (b) Yes
  20. 20.In triangle ABC, angle A = 22° and angle B = 26°. What is angle C (in degrees)?
  21. 21.The angles of a triangle are in the ratio 1 : 2 : 6. What is the biggest angle (in degrees)?
  22. 22.In a right-angled triangle, one of the other two angles is 54°. What is the third angle (in degrees)?
  23. 23.An exterior angle of a triangle is 64°. One of its two interior opposite angles is 24°. What is the other one (in degrees)?
  24. 24.In an isosceles triangle, the two equal angles are 84° each. What is the third angle (in degrees)?
  25. 25.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)?
  26. 26.In a right-angled triangle, one of the other two angles is 61°. What is the third angle (in degrees)?
  27. 27.Can a triangle have sides of 11 cm, 9 cm and 6 cm? (a) Yes (b) No
  28. 28.In triangle ABC, angle A = 58° and angle B = 79°. What is angle C (in degrees)?
  29. 29.Can a triangle have sides of 14 cm, 11 cm and 9 cm? (a) No (b) Yes
  30. 30.The two shorter sides of a right-angled triangle are 20 cm and 15 cm. How long is the longest side (in cm)?
  31. 31.In an isosceles triangle, the angle between the two equal sides is 36°. What is each of the other two angles (in degrees)?
  32. 32.The two interior opposite angles of a triangle are 59° and 68°. What is the exterior angle (in degrees)?
  33. 33.In a right-angled triangle, one of the other two angles is 65°. What is the third angle (in degrees)?
  34. 34.In a right-angled triangle, one of the other two angles is 19°. What is the third angle (in degrees)?
  35. 35.Can a triangle have sides of 23 cm, 9 cm and 11 cm? (a) No (b) Yes
  36. 36.Can a triangle have sides of 6 cm, 10 cm and 11 cm? (a) Yes (b) No
  37. 37.In an isosceles triangle, the angle between the two equal sides is 146°. What is each of the other two angles (in degrees)?
  38. 38.In a right-angled triangle, one of the other two angles is 35°. What is the third angle (in degrees)?
  39. 39.The angles of a triangle are in the ratio 1 : 3 : 5. What is the smallest angle (in degrees)?
  40. 40.In triangle ABC, angle A = 54° and angle B = 35°. What is angle C (in degrees)?

Answer key

  1. 138
  2. 40
  3. 31
  4. 21
  5. 90
  6. 90
  7. 66
  8. 80
  9. 95
  10. 45
  11. 100
  12. 44
  13. 65
  14. 90
  15. No
  16. 43
  17. 128
  18. 62
  19. Yes
  20. 132
  21. 120
  22. 36
  23. 40
  24. 12
  25. 15
  26. 29
  27. Yes
  28. 43
  29. Yes
  30. 25
  31. 72
  32. 127
  33. 25
  34. 71
  35. No
  36. Yes
  37. 17
  38. 55
  39. 20
  40. 91

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