\r\n" );
document.write( "Get some graph paper and plot the lines:\r\n" );
document.write( "\r\n" );
document.write( "
\r\n" );
document.write( "\r\n" );
document.write( "The red line is the line 2x-y-1=0, eq.1\r\n" );
document.write( "The blue line is the line 3x+y-4=0, eq.2\r\n" );
document.write( "\r\n" );
document.write( "They cross at the point (1,1)\r\n" );
document.write( "\r\n" );
document.write( "Notice that to get from the point where they cross (1,1)\r\n" );
document.write( "we have to go left 1 unit and then up 3 units. That's\r\n" );
document.write( "indicated by the green lines:\r\n" );
document.write( "\r\n" );
document.write( "
\r\n" );
document.write( "\r\n" );
document.write( "Now this time starting at (1,1) and go right as many units\r\n" );
document.write( "as you went up before, and up as many units as you went\r\n" );
document.write( "left before, like the other green lines below:\r\n" );
document.write( "\r\n" );
document.write( "
\r\n" );
document.write( "\r\n" );
document.write( "You see that you ended up at the point (4,2).\r\n" );
document.write( "\r\n" );
document.write( "Now draw a line through (1,1) and (4,2), like this black\r\n" );
document.write( "line below:\r\n" );
document.write( "\r\n" );
document.write( "
\r\n" );
document.write( "\r\n" );
document.write( "That black line is the line which is symmetric to eq. 2 with\r\n" );
document.write( "respect to eq. 1. \r\n" );
document.write( "\r\n" );
document.write( "We find its equation. It goes through (1,1) and (4,2).\r\n" );
document.write( "\r\n" );
document.write( "We use the slope formula:\r\n" );
document.write( "\r\n" );
document.write( "




.\r\n" );
document.write( "\r\n" );
document.write( "Then we use the point-slope form:\r\n" );
document.write( "\r\n" );
document.write( "

\r\n" );
document.write( "\r\n" );
document.write( "

\r\n" );
document.write( "\r\n" );
document.write( "Multiply through by 3\r\n" );
document.write( "\r\n" );
document.write( "

\r\n" );
document.write( "\r\n" );
document.write( "
\r\n" );
document.write( "\r\n" );
document.write( "or, multiplying by -1\r\n" );
document.write( "\r\n" );
document.write( "
<-- the equation of the black line.\r\n" );
document.write( "\r\n" );
document.write( "Edwin
\n" );
document.write( "