document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=1124978>Question 1124978</A>: <I><SPAN STYLE=\"word-break: break-all;\"> a + b + c + d = 7 <BR>\n" );
document.write( "2a - b + c - 2d= -13<BR>\n" );
document.write( "3a + b - 2c - d = 5 <BR>\n" );
document.write( "4a - b + 3c - d = -10 <BR>\n" );
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document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #741310 by </B><A HREF=/tutors/aboutme.mpl?userid=math_helper><B>math_helper(2461)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=math_helper><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=math_helper><BR>You can <A HREF=\"/cgi-bin/embed-solution.mpl?show=1&solution=741310\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=+%28matrix%284%2C4%2C+1%2C1%2C1%2C1%2C++2%2C-1%2C1%2C-2%2C+3%2C1%2C-2%2C-1%2C+4%2C-1%2C3%2C-1%29%29+%2A+%28matrix%284%2C1%2C++a%2Cb%2Cc%2Cd%29%29+=+%28matrix%284%2C1%2C+7%2C-13%2C5%2C-10%29+%29+ ALIGN=MIDDLE   DISABLED_style= \"max-width:90%; height:auto;\" ><br>\r<BR>\n" );
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document.write( "We have  <b>Ax = b</b> and the solution we want is  <b>BAx=Bb</b>  where B is <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=A%5E-1 ALIGN=MIDDLE  ALT=\"A%5E-1\"   DISABLED_style= \"max-width:90%; height:auto;\" ><br>\r<BR>\n" );
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document.write( "Using your favorite matrix inverter website and/or computing by hand:<BR>\n" );
document.write( "B = <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=+%281%2F19%29%2A%28matrix%284%2C4%2C+-5%2C-8%2C4%2C7%2C+25%2C21%2C-1%2C-16%2C++11%2C10%2C-5%2C-4%2C++-12%2C-23%2C2%2C13%29%29+ ALIGN=MIDDLE   DISABLED_style= \"max-width:90%; height:auto;\" > <br>\r<BR>\n" );
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document.write( "So <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=+%28matrix%284%2C1%2C+a%2Cb%2Cc%2Cd%29%29+=+%281%2F19%29%2A%28matrix%284%2C4%2C+-5%2C-8%2C4%2C7%2C+25%2C21%2C-1%2C-16%2C++11%2C10%2C-5%2C-4%2C++-12%2C-23%2C2%2C13%29%29%2A+%28matrix%284%2C1%2C+7%2C-13%2C5%2C-10%29%29+ ALIGN=MIDDLE   DISABLED_style= \"max-width:90%; height:auto;\" > ==>  <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=+highlight%28+%28matrix%284%2C1%2C+a%2Cb%2Cc%2Cd%29%29+=++%28matrix%284%2C1%2C+1%2C3%2C-2%2C5%29%29+%29+ ALIGN=MIDDLE   DISABLED_style= \"max-width:90%; height:auto;\" > <br>\r<BR>\n" );
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document.write( "Check: <BR>\n" );
document.write( "  1+3+(-2)+5 = 7 (ok)<BR>\n" );
document.write( "  2(1)-3+(-2)-2(5) = -13 (ok)<BR>\n" );
document.write( "  3(1)+3-2(-2)-5 = 5  (ok)       <BR>\n" );
document.write( "  4(1)-3+3(-2)-5 = -10 (ok)<BR>\n" );
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