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Class 7 Maths Worksheet: Triangles

Maths worksheets lesson 53: Triangles: angle sum, exterior angle and Pythagoras · Set 291 · 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 30° each. What is the third angle (in degrees)?
  2. 2.In a right-angled triangle, one of the other two angles is 71°. What is the third angle (in degrees)?
  3. 3.The angles of a triangle are in the ratio 1 : 2 : 3. What is the biggest angle (in degrees)?
  4. 4.In triangle ABC, angle A = 100° and angle B = 39°. What is angle C (in degrees)?
  5. 5.Can a triangle have sides of 12 cm, 10 cm and 20 cm? (a) Yes (b) No
  6. 6.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)?
  7. 7.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)?
  8. 8.The two shorter sides of a right-angled triangle are 7 cm and 24 cm. How long is the longest side (in cm)?
  9. 9.In a right-angled triangle, one of the other two angles is 53°. What is the third angle (in degrees)?
  10. 10.The angles of a triangle are in the ratio 3 : 4 : 5. What is the biggest angle (in degrees)?
  11. 11.Can a triangle have sides of 6 cm, 9 cm and 9 cm? (a) No (b) Yes
  12. 12.The angles of a triangle are in the ratio 1 : 3 : 5. What is the smallest angle (in degrees)?
  13. 13.The two interior opposite angles of a triangle are 56° and 77°. What is the exterior angle (in degrees)?
  14. 14.The two shorter sides of a right-angled triangle are 15 cm and 8 cm. How long is the longest side (in cm)?
  15. 15.In triangle ABC, angle A = 93° and angle B = 28°. What is angle C (in degrees)?
  16. 16.In a right-angled triangle, one of the other two angles is 52°. What is the third angle (in degrees)?
  17. 17.In an isosceles triangle, the angle between the two equal sides is 134°. What is each of the other two angles (in degrees)?
  18. 18.An exterior angle of a triangle is 101°. One of its two interior opposite angles is 25°. What is the other one (in degrees)?
  19. 19.The two shorter sides of a right-angled triangle are 24 cm and 10 cm. How long is the longest side (in cm)?
  20. 20.An exterior angle of a triangle is 82°. One of its two interior opposite angles is 23°. What is the other one (in degrees)?
  21. 21.The angles of a triangle are in the ratio 2 : 3 : 4. What is the biggest angle (in degrees)?
  22. 22.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)?
  23. 23.Can a triangle have sides of 6 cm, 17 cm and 7 cm? (a) No (b) Yes
  24. 24.In a right-angled triangle, one of the other two angles is 17°. What is the third angle (in degrees)?
  25. 25.In an isosceles triangle, the two equal angles are 25° each. What is the third angle (in degrees)?
  26. 26.In an isosceles triangle, the two equal angles are 52° each. What is the third angle (in degrees)?
  27. 27.Can a triangle have sides of 6 cm, 7 cm and 12 cm? (a) Yes (b) No
  28. 28.The two interior opposite angles of a triangle are 78° and 66°. What is the exterior angle (in degrees)?
  29. 29.The two interior opposite angles of a triangle are 59° and 71°. What is the exterior angle (in degrees)?
  30. 30.In an isosceles triangle, the two equal angles are 67° each. What is the third angle (in degrees)?
  31. 31.In triangle ABC, angle A = 52° and angle B = 47°. What is angle C (in degrees)?
  32. 32.The angles of a triangle are in the ratio 2 : 3 : 5. What is the smallest angle (in degrees)?
  33. 33.In triangle ABC, angle A = 22° and angle B = 74°. What is angle C (in degrees)?
  34. 34.In an isosceles triangle, the two equal angles are 57° each. What is the third angle (in degrees)?
  35. 35.In triangle ABC, angle A = 25° and angle B = 53°. What is angle C (in degrees)?
  36. 36.In triangle ABC, angle A = 71° and angle B = 81°. What is angle C (in degrees)?
  37. 37.In triangle ABC, angle A = 98° and angle B = 34°. What is angle C (in degrees)?
  38. 38.In triangle ABC, angle A = 81° and angle B = 58°. What is angle C (in degrees)?
  39. 39.The two interior opposite angles of a triangle are 63° and 72°. What is the exterior angle (in degrees)?
  40. 40.The longest side of a right-angled triangle is 25 cm and one of the other sides is 7 cm. How long is the third side (in cm)?

Answer key

  1. 120
  2. 19
  3. 90
  4. 41
  5. Yes
  6. 7
  7. 5
  8. 25
  9. 37
  10. 75
  11. Yes
  12. 20
  13. 133
  14. 17
  15. 59
  16. 38
  17. 23
  18. 76
  19. 26
  20. 59
  21. 80
  22. 15
  23. No
  24. 73
  25. 130
  26. 76
  27. Yes
  28. 144
  29. 130
  30. 46
  31. 81
  32. 36
  33. 84
  34. 66
  35. 102
  36. 28
  37. 48
  38. 41
  39. 135
  40. 24

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