document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=1031838>Question 1031838</A>: <I><SPAN STYLE=\"word-break: break-all;\"> An airplane flies 250 km against the wind and 680 km with the wind in a total time of 4 hour. The speed of the airplane is 300 km/h. What is the speed of the wind?  </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #646548 by </B><A HREF=/tutors/aboutme.mpl?userid=Alan3354><B>Alan3354(69443)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=Alan3354><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=Alan3354><BR>You can <A HREF=\"/cgi-bin/embed-solution.mpl?show=1&solution=646548\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> An airplane flies 250 km against the wind and 680 km with the wind in a total time of 4 hour. The speed of the airplane is 300 km/h. What is the speed of the wind? <BR>\n" );
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document.write( "a = plane's airspeed = 300<BR>\n" );
document.write( "w = windspeed<BR>\n" );
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document.write( "250/(300-w) + 680/(300+w) = 4<BR>\n" );
document.write( "250*(300+w) + 680*(300-w) = 4*(300+w)*(300-w) = 360000 - 4w^2<BR>\n" );
document.write( "75000 + 204000 - 430w = 360000 - 4w^2<BR>\n" );
document.write( "4w^2 - 430w - 81000 = 0<BR>\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=solve_quadratic_equation.solver>SOLVE quadratic equation (work shown, graph etc)</A></TD></TR>\n" );
document.write( "<TR><TD  ALIGN=LEFT>Quadratic equation <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=ax%5E2%2Bbx%2Bc=0 ALIGN=MIDDLE  ALT=\"ax%5E2%2Bbx%2Bc=0\"   DISABLED_style= \"max-width:90%; height:auto;\" > (in our case <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=4x%5E2%2B-430x%2B-81000+=+0 ALIGN=MIDDLE  ALT=\"4x%5E2%2B-430x%2B-81000+=+0\"   DISABLED_style= \"max-width:90%; height:auto;\" >) has the following solutons:<BR>\n" );
document.write( "  <BR>\n" );
document.write( "  <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=x%5B12%5D+=+%28b%2B-sqrt%28+b%5E2-4ac+%29%29%2F2%5Ca ALIGN=MIDDLE  ALT=\"x%5B12%5D+=+%28b%2B-sqrt%28+b%5E2-4ac+%29%29%2F2%5Ca\"   DISABLED_style= \"max-width:90%; height:auto;\" ><BR>\n" );
document.write( "  <BR>\n" );
document.write( "  For these solutions to exist, the <U>discriminant</U> <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=b%5E2-4ac ALIGN=MIDDLE  ALT=\"b%5E2-4ac\"   DISABLED_style= \"max-width:90%; height:auto;\" > should not be a negative number.<BR>\n" );
document.write( "  <BR>\n" );
document.write( "  First, we need to compute the discriminant <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=b%5E2-4ac ALIGN=MIDDLE  ALT=\"b%5E2-4ac\"   DISABLED_style= \"max-width:90%; height:auto;\" >: <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=b%5E2-4ac=%28-430%29%5E2-4%2A4%2A-81000=1480900 ALIGN=MIDDLE  ALT=\"b%5E2-4ac=%28-430%29%5E2-4%2A4%2A-81000=1480900\"   DISABLED_style= \"max-width:90%; height:auto;\" >.<BR>\n" );
document.write( "  <BR>\n" );
document.write( "  Discriminant d=1480900 is greater than zero. That means that there are two solutions: <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=+x%5B12%5D+=+%28--430%2B-sqrt%28+1480900+%29%29%2F2%5Ca ALIGN=MIDDLE  ALT=\"+x%5B12%5D+=+%28--430%2B-sqrt%28+1480900+%29%29%2F2%5Ca\"   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=x%5B1%5D+=+%28-%28-430%29%2Bsqrt%28+1480900+%29%29%2F2%5C4+=+205.865293445465 ALIGN=MIDDLE  ALT=\"x%5B1%5D+=+%28-%28-430%29%2Bsqrt%28+1480900+%29%29%2F2%5C4+=+205.865293445465\"   DISABLED_style= \"max-width:90%; height:auto;\" ><BR>\n" );
document.write( "    <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=x%5B2%5D+=+%28-%28-430%29-sqrt%28+1480900+%29%29%2F2%5C4+=+-98.3652934454652 ALIGN=MIDDLE  ALT=\"x%5B2%5D+=+%28-%28-430%29-sqrt%28+1480900+%29%29%2F2%5C4+=+-98.3652934454652\"   DISABLED_style= \"max-width:90%; height:auto;\" ><BR>\n" );
document.write( "    <BR>\n" );
document.write( "    Quadratic expression <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=4x%5E2%2B-430x%2B-81000 ALIGN=MIDDLE  ALT=\"4x%5E2%2B-430x%2B-81000\"   DISABLED_style= \"max-width:90%; height:auto;\" > can be factored:<BR>\n" );
document.write( "  <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=4x%5E2%2B-430x%2B-81000+=+%28x-205.865293445465%29%2A%28x--98.3652934454652%29 ALIGN=MIDDLE  ALT=\"4x%5E2%2B-430x%2B-81000+=+%28x-205.865293445465%29%2A%28x--98.3652934454652%29\"   DISABLED_style= \"max-width:90%; height:auto;\" ><BR>\n" );
document.write( "  Again, the answer is: 205.865293445465, -98.3652934454652.\n" );
document.write( "Here's your graph:<BR>\n" );
document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=graph%28+500%2C+500%2C+-10%2C+10%2C+-20%2C+20%2C+4%2Ax%5E2%2B-430%2Ax%2B-81000+%29 ALIGN=MIDDLE  ALT=\"graph%28+500%2C+500%2C+-10%2C+10%2C+-20%2C+20%2C+4%2Ax%5E2%2B-430%2Ax%2B-81000+%29\"   DISABLED_style= \"max-width:90%; height:auto;\" ></TD></TR>\n" );
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document.write( "w =~ 206 km/hr<BR>\n" );
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document.write( "No fun flying upwind like that.<BR>\n" );
document.write( "Downwind is great. </SPAN>\n" );
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