<PRE><B>Question 915784</B>
proof:


1.    &lt;{{{1}}} +&lt;{{{2}}} = {{{180}}}=&gt;given  supplementary

2.   &lt;{{{3}}} +&lt;{{{4}}} = {{{180}}}=&gt;given  supplementary

3.  &lt;{{{2}}} = {{{180}}}- &lt;{{{1}}}=&gt;subst  postulate

4.  &lt;{{{3}}} = {{{180}}}- &lt;{{{4}}}=&gt;subst  postulate

5   &lt;{{{2 }}}= &lt;{{{3}}}=&gt;given

6  {{{180}}}-&lt;{{{1 }}}= {{{180}}}-&lt;{{{4}}}=&gt;substitution

7  &lt;{{{1}}} = &lt;{{{4}}}=&gt;subtraction  and  multiplication  postulate

.
Note:  There  is  a  Theorem  that  &quot; if  {{{2}}}  angles  are  supplements  of  equal  angles, then the  two  angles  {{{are}}}{{{  congruent}}}&quot;

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