Question 1099022
.
In a normal geometric language this statements says:


<pre>
    If in a quadrilateral the opposite sides are congruent, then the opposite angles are congruent.
</pre>

If you know the basic facts of Geometry, then the proof is in two steps:


<pre>
    1.  If in a quadrilateral the opposite sides are congruent, then the quadrilateral is a parallelogram.

        For the proof, see the lesson 
            <A HREF=https://www.algebra.com/algebra/homework/Parallelograms/Properties-of-the-sides-of-a-parallelogram.lesson>Properties of the sides of a parallelogram</A>, Theorem 2
        in this site.


    2.  In a parallelogram, the opposite angles are congruent.

        For the proof, see the lesson 
            <A HREF=https://www.algebra.com/algebra/homework/Parallelograms/Opposite-angles-of-a-parallelogram-are-congruent.lesson>Opposite angles of a parallelogram</A>, Theorem 1
        in this site.
</pre>


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In this site, &nbsp;you have this free of charge online textbook on Geometry

&nbsp;&nbsp;&nbsp;&nbsp;<A HREF=https://www.algebra.com/algebra/homework/Triangles/GEOMETRY-your-online-textbook.lesson>GEOMETRY - YOUR ONLINE TEXTBOOK</A> 


The referred lessons are the part of this online textbook under the topic &nbsp;"<U>Properties of parallelograms</U>".



Save the link to this online textbook together with its description


Free of charge online textbook in GEOMETRY
https://www.algebra.com/algebra/homework/Triangles/GEOMETRY-your-online-textbook.lesson


to your archive and use it when it is needed.