document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=1015007>Question 1015007</A>: <I><SPAN STYLE=\"word-break: break-all;\"> Thanks!\r<BR>\n" );
document.write( "\n" );
document.write( "In which line is a mistake first made when solving the following system of equations by substitution?<BR>\n" );
document.write( "3x + y = 9<BR>\n" );
document.write( "-2x + y = 4\r<BR>\n" );
document.write( "<BR>\n" );
document.write( "<BR>\n" );
document.write( "\n" );
document.write( "Line 1<BR>\n" );
document.write( "y = -3x + 9<BR>\n" );
document.write( "-2x + y = 4<BR>\n" );
document.write( "Line 2<BR>\n" );
document.write( "3x + (-3x + 9) = 9<BR>\n" );
document.write( "Line 3<BR>\n" );
document.write( "3x - 3x + 9 = 9<BR>\n" );
document.write( "Line 4<BR>\n" );
document.write( "9 = 9 </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #631327 by </B><A HREF=/tutors/aboutme.mpl?userid=ValorousDawn><B>ValorousDawn(53)</B></A><img src=\"/images/stars/stars-08.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=ValorousDawn><IMG SRC=http://www.algebra.com/images/aboutme-small.gif BORDER=0 alt=\"About Me\" VALIGN=MIDDLE></A>&nbsp;<IMG SRC=http://www.algebra.com/cgi-bin/show-face.mpl?user=ValorousDawn><BR>You can <A HREF=\"/cgi-bin/embed-solution.mpl?show=1&solution=631327\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> Line 2. You don't plug in a variable's identity back into the original equation. \r<BR>\n" );
document.write( "\n" );
document.write( "Otherwise, you get a useless statement, as above with 9=9 Given a linear equation <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=ax%2Bby=c ALIGN=MIDDLE  ALT=\"ax%2Bby=c\"   DISABLED_style= \"max-width:90%; height:auto;\" >, and one isolates a term, for example, the y as such <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=by=-ax%2Bc ALIGN=MIDDLE  ALT=\"by=-ax%2Bc\"   DISABLED_style= \"max-width:90%; height:auto;\" > then <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=y=-ax%2Fb%2Bc%2Fb ALIGN=MIDDLE  ALT=\"y=-ax%2Fb%2Bc%2Fb\"   DISABLED_style= \"max-width:90%; height:auto;\" >. If you were to plug this back into the equation, you'd get <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=ax%2Bb%28-ax%2Fb%2Bc%2Fb%29=c ALIGN=MIDDLE  ALT=\"ax%2Bb%28-ax%2Fb%2Bc%2Fb%29=c\"   DISABLED_style= \"max-width:90%; height:auto;\" >, then <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=ax-ax%2Bc=c ALIGN=MIDDLE  ALT=\"ax-ax%2Bc=c\"   DISABLED_style= \"max-width:90%; height:auto;\" > which is then <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=c=c ALIGN=MIDDLE  ALT=\"c=c\"   DISABLED_style= \"max-width:90%; height:auto;\" >. \r<BR>\n" );
document.write( "\n" );
document.write( "In this case, you'd plug in the equation for y <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=y=-3x%2B9 ALIGN=MIDDLE  ALT=\"y=-3x%2B9\"   DISABLED_style= \"max-width:90%; height:auto;\" > into the OTHER equation. This gives you <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=-2x%2B%28-3x%2B9%29=4 ALIGN=MIDDLE  ALT=\"-2x%2B%28-3x%2B9%29=4\"   DISABLED_style= \"max-width:90%; height:auto;\" > which gives you <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=-5x=-5 ALIGN=MIDDLE  ALT=\"-5x=-5\"   DISABLED_style= \"max-width:90%; height:auto;\" > or <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=x=1 ALIGN=MIDDLE  ALT=\"x=1\"   DISABLED_style= \"max-width:90%; height:auto;\" >. You then plug this into your equation for y, and solve. <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=y=-3%281%29%2B9 ALIGN=MIDDLE  ALT=\"y=-3%281%29%2B9\"   DISABLED_style= \"max-width:90%; height:auto;\" > <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=y=6 ALIGN=MIDDLE  ALT=\"y=6\"   DISABLED_style= \"max-width:90%; height:auto;\" > </SPAN>\n" );
document.write( "</TD></TR></TABLE>\n" );