Answers

2015-12-15T00:55:29+05:30
The theorem
"If a transversal intersects two parallel lines, then each pair of alternate interior angles are equal. "
proves that alternate angles are equal
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2015-12-20T14:53:54+05:30
Take two parralel line segments.

Lets say AB & CD are parallel . & AB = CD

Now draw a transversal AD .

Now join AC & BD.

We find that traingle ACD is congruent to traingle BDC ( SSS ) .

BY CPCT we find alternate amgles are equal.

This is generalized as a theory . Because even if AB is not equal to CD , you can always construct this and you will get a rectangle with the transversal as its diagonal. In a rectangles the two triangles divided by diagonal are congruent . Thus alternate angles are equal.
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