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If two parallel lines are intersected by a transversal, then prove that the bisectors of any pair of alternate interior angles are parallel?
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Proof that the bisectors of any pair of alternate interior angles are parallel

Given: Two parallel lines intersected by a transversal

To prove: The bisectors of any pair of alternate interior angles are parallel

Proof:


  1. Let AB and CD be two parallel lines intersected by a transversal EF at point G.

  2. Let H be a point on line EF, and let angles AHD and BGC be alternate interior angles.

  3. Let AI be the bisector of angle AHD and BJ be the bisector of angle BGC.

  4. Let JI intersect line EF at point K.

  5. Since AI bisects angle AHD, we have angle AHI = angle IHD.

  6. Similarly, since BJ bisects angle BGC, we have angle BJG = angle JGC.

  7. Since AB and CD are parallel lines, we have angle AHI = angle BJG (alternate interior angles).

  8. Therefore, angle IHD = angle JGC.

  9. Since angles IHD and JGC are corresponding angles formed by parallel lines, they are equal.

  10. Therefore, angles JKI and IKH are equal.

  11. Since the sum of angles in a triangle is 180 degrees, we have angle JKG + angle GKI + angle IKH = 180 degrees.

  12. Substituting angle JGC for angle AHI, we have angle JKG + angle GKI + angle JGC = 180 degrees.

  13. Therefore, angle JKG + angle GKI + angle JKI = 180 degrees.

  14. Since angles JKI and IKH are equal, we have angle JKG + angle GKI + angle IKH = 180 degrees.

  15. Therefore, angle JKG + angle GKI + angle JKG = 180 degrees.

  16. Therefore, the sum of angles JKG and GKI is equal to 180 degrees.

  17. Therefore, the lines JI and EF are parallel.

  18. Therefore, the bisectors of any pair of alternate interior angles are parallel.



Conclusion: Therefore, we have proved that the bisectors of any pair of alternate interior angles are parallel when two parallel lines are intersected by a transversal.
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If two parallel lines are intersected by a transversal, then prove that the bisectors of any pair of alternate interior angles are parallel?
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