document.write( "Question 1081439: Thank you for your help in advance.\r
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\n" ); document.write( "Prove the opposite angles of a parallelogram are congruent.
\n" ); document.write( "Prove the base angles of an isosceles triangle are congruent.
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Algebra.Com's Answer #695489 by MathLover1(20850)\"\" \"About 
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\n" ); document.write( "\n" ); document.write( "Start with the following isosceles triangle. The two equal sides are shown with one red mark and the angles opposites to these sides are also shown in red.\r
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\n" ); document.write( "\n" ); document.write( "The strategy is to draw the perpendicular bisector from vertex \"C\" to segment \"AB\".\r
\n" ); document.write( "\n" ); document.write( "Then use \"SAS\" postulate to show that the two triangles formed are congruent.\r
\n" ); document.write( "\n" ); document.write( "If the two triangles are congruent, then corresponding angles to will be congruent.\r
\n" ); document.write( "\n" ); document.write( "Draw the perpendicular bisector from \"C\".\r
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\n" ); document.write( "\n" ); document.write( "Since angle \"C\" is bisected,we got\r
\n" ); document.write( "\n" ); document.write( "angle \"x\" and angle \"y\" which are same measure; so, angle \"+x=+y\"\r
\n" ); document.write( "\n" ); document.write( "Segment \"AC+=++BC\"... ( This one was \"given\")\r
\n" ); document.write( "\n" ); document.write( "Segment \"CF+=+CF+\"(Common side is the same for both triangle \"ACF\" and triangle \"BCF\")\r
\n" ); document.write( "\n" ); document.write( "Triangles \"ACF\" and triangle \"BCF\" are then congruent by \"SAS\" or \"side-angle-side\".\r
\n" ); document.write( "\n" ); document.write( "In other words, by\r
\n" ); document.write( "\n" ); document.write( "\"AC\"-angle(\"x\")-\"CF\"\r
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\n" ); document.write( "\n" ); document.write( "\"BC\"-angle(\"y\")-\"CF\"\r
\n" ); document.write( "\n" ); document.write( "Since triangle \"ACF\" and triangle \"BCF\" are congruent, angle \"A\" = angle\"+B\"\r
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