document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=904332>Question 904332</A>: <I><SPAN STYLE=\"word-break: break-all;\"> use completing the square to solve 2x^2-4x-5=0 I am so rusty but i am sure i will remember once it starts to look familiar again </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #548629 by </B><A HREF=/tutors/aboutme.mpl?userid=richwmiller><B>richwmiller(17219)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=richwmiller><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=richwmiller><BR>You can <A HREF=\"/cgi-bin/embed-solution.mpl?show=1&solution=548629\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> <TABLE  BORDER=1>\n" );
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document.write( " <TR><TD  ALIGN=MIDDLE>Solved by <A  rel=nofollow HREF=http://wiki.algebra.com/index.php/Tutoring_-_pluggable_solvers>pluggable</A> solver: <A  rel=nofollow HREF=complete_square.solver>COMPLETING THE SQUARE solver for quadratics</A></TD></TR>\n" );
document.write( "<TR><TD  ALIGN=LEFT>Read <A  rel=nofollow HREF=Fool-Proof-Completing-the-Square-Part-I.lesson>this lesson on completing the square by prince_abubu</A>, if you do not know how to complete the square.<BR>Let's convert <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=2x%5E2%2B-4x%2B-5=0 ALIGN=MIDDLE  ALT=\"2x%5E2%2B-4x%2B-5=0\"   DISABLED_style= \"max-width:90%; height:auto;\" > to standard form by dividing both sides by 2: <BR>\n" );
document.write( "We have: <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=1x%5E2%2B-2x%2B-2.5=0 ALIGN=MIDDLE  ALT=\"1x%5E2%2B-2x%2B-2.5=0\"   DISABLED_style= \"max-width:90%; height:auto;\" >. \n" );
document.write( "What we want to do now is to change this equation to a complete square <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=%28x%2Bsomenumber%29%5E2+%2B+othernumber ALIGN=MIDDLE  ALT=\"%28x%2Bsomenumber%29%5E2+%2B+othernumber\"   DISABLED_style= \"max-width:90%; height:auto;\" >. How can we find out values of <B>somenumber</B> and <B>othernumber</B> that would make it work?<BR>\n" );
document.write( "Look at <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=%28x%2Bsomenumber%29%5E2 ALIGN=MIDDLE  ALT=\"%28x%2Bsomenumber%29%5E2\"   DISABLED_style= \"max-width:90%; height:auto;\" >: <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=%28x%2Bsomenumber%29%5E2+=+x%5E2%2B2%2Asomenumber%2Ax+%2B+somenumber%5E2 ALIGN=MIDDLE  ALT=\"%28x%2Bsomenumber%29%5E2+=+x%5E2%2B2%2Asomenumber%2Ax+%2B+somenumber%5E2\"   DISABLED_style= \"max-width:90%; height:auto;\" >. Since the coefficient in our equation <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=1x%5E2%2Bhighlight_red%28+-2%29+%2A+x%2B-2.5=0 ALIGN=MIDDLE  ALT=\"1x%5E2%2Bhighlight_red%28+-2%29+%2A+x%2B-2.5=0\"   DISABLED_style= \"max-width:90%; height:auto;\" > that goes in front of x is -2, we know that -2=2*somenumber, or <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=somenumber+=+-2%2F2 ALIGN=MIDDLE  ALT=\"somenumber+=+-2%2F2\"   DISABLED_style= \"max-width:90%; height:auto;\" >. So, we know that our equation can be rewritten as <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=%28x%2B-2%2F2%29%5E2+%2B+othernumber ALIGN=MIDDLE  ALT=\"%28x%2B-2%2F2%29%5E2+%2B+othernumber\"   DISABLED_style= \"max-width:90%; height:auto;\" >, and we do not yet know the other number.<BR>\n" );
document.write( "We are almost there. Finding the other number is simply a matter of not making too many mistakes. We need to find 'other number' such that  <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=%28x%2B-2%2F2%29%5E2+%2B+othernumber ALIGN=MIDDLE  ALT=\"%28x%2B-2%2F2%29%5E2+%2B+othernumber\"   DISABLED_style= \"max-width:90%; height:auto;\" > is equivalent to our original equation <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=1x%5E2%2B-2x%2Bhighlight_green%28+-2.5+%29=0 ALIGN=MIDDLE  ALT=\"1x%5E2%2B-2x%2Bhighlight_green%28+-2.5+%29=0\"   DISABLED_style= \"max-width:90%; height:auto;\" >.<BR>\n" );
document.write( "  <BR>\n" );
document.write( "  <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=%28x%2B-2%2F2%29%5E2+%2B+othernumber+=+x%5E2%2B-2x%2Bhighlight_red%28+-2%5E2%2F4%2Bothernumber+%29 ALIGN=MIDDLE   DISABLED_style= \"max-width:90%; height:auto;\" ><BR>\n" );
document.write( "  The highlighted <FONT COLOR=red>red part</FONT> must be equal to -2.5 (highlighted <FONT COLOR=green>green part</FONT>).<BR>\n" );
document.write( "  <BR>\n" );
document.write( "  <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=-2%5E2%2F4+%2B+othernumber+=+-2.5 ALIGN=MIDDLE  ALT=\"-2%5E2%2F4+%2B+othernumber+=+-2.5\"   DISABLED_style= \"max-width:90%; height:auto;\" >, or <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=othernumber+=+-2.5--2%5E2%2F4+=+-3.5 ALIGN=MIDDLE  ALT=\"othernumber+=+-2.5--2%5E2%2F4+=+-3.5\"   DISABLED_style= \"max-width:90%; height:auto;\" >.<BR>\n" );
document.write( "So, the equation converts to <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=%28x%2B-2%2F2%29%5E2+%2B+-3.5+=+0 ALIGN=MIDDLE  ALT=\"%28x%2B-2%2F2%29%5E2+%2B+-3.5+=+0\"   DISABLED_style= \"max-width:90%; height:auto;\" >, or <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=%28x%2B-2%2F2%29%5E2+=+3.5 ALIGN=MIDDLE  ALT=\"%28x%2B-2%2F2%29%5E2+=+3.5\"   DISABLED_style= \"max-width:90%; height:auto;\" >.<BR>\n" );
document.write( "  <BR>\n" );
document.write( "    Our equation converted to a square <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=%28x%2B-2%2F2%29%5E2 ALIGN=MIDDLE  ALT=\"%28x%2B-2%2F2%29%5E2\"   DISABLED_style= \"max-width:90%; height:auto;\" >, equated to a number (3.5).<BR>\n" );
document.write( "  <BR>\n" );
document.write( "    Since the right part 3.5 is greater than zero, there are two solutions:<BR>\n" );
document.write( "  <BR>\n" );
document.write( "     <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=system%28+%28x%2B-2%2F2%29+=+%2Bsqrt%28+3.5+%29%2C+%28x%2B-2%2F2%29+=+-sqrt%28+3.5+%29+%29 ALIGN=MIDDLE  ALT=\"system%28+%28x%2B-2%2F2%29+=+%2Bsqrt%28+3.5+%29%2C+%28x%2B-2%2F2%29+=+-sqrt%28+3.5+%29+%29\"   DISABLED_style= \"max-width:90%; height:auto;\" ><BR>\n" );
document.write( "    , or<BR>\n" );
document.write( "  <BR>\n" );
document.write( "     <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=system%28+%28x%2B-2%2F2%29+=+1.87082869338697%2C+%28x%2B-2%2F2%29+=+-1.87082869338697+%29 ALIGN=MIDDLE  ALT=\"system%28+%28x%2B-2%2F2%29+=+1.87082869338697%2C+%28x%2B-2%2F2%29+=+-1.87082869338697+%29\"   DISABLED_style= \"max-width:90%; height:auto;\" ><BR>\n" );
document.write( "     <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=system%28+x%2B-2%2F2+=+1.87082869338697%2C+x%2B-2%2F2+=+-1.87082869338697+%29 ALIGN=MIDDLE  ALT=\"system%28+x%2B-2%2F2+=+1.87082869338697%2C+x%2B-2%2F2+=+-1.87082869338697+%29\"   DISABLED_style= \"max-width:90%; height:auto;\" ><BR>\n" );
document.write( "     <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=system%28+x+=+1.87082869338697--2%2F2%2C+x+=+-1.87082869338697--2%2F2+%29 ALIGN=MIDDLE  ALT=\"system%28+x+=+1.87082869338697--2%2F2%2C+x+=+-1.87082869338697--2%2F2+%29\"   DISABLED_style= \"max-width:90%; height:auto;\" ><BR>\n" );
document.write( "    <BR>\n" );
document.write( "     <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=system%28+x+=+2.87082869338697%2C+x+=+-0.870828693386971+%29 ALIGN=MIDDLE  ALT=\"system%28+x+=+2.87082869338697%2C+x+=+-0.870828693386971+%29\"   DISABLED_style= \"max-width:90%; height:auto;\" ><BR>\n" );
document.write( "Answer: x=2.87082869338697, -0.870828693386971.\n" );
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