document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=1122879>Question 1122879</A>: <I><SPAN STYLE=\"word-break: break-all;\"> Find the equation of the focal chord that cuts the curve y^2 = 16x at (4,8) </SPAN>\n" );
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document.write( "The graph is a parabola with vertex at (0,0) that opens to the right.  One standard form of the equation is<br><BR>\n" );
document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=x+=+%281%2F%284p%29%29y%5E2 ALIGN=MIDDLE  ALT=\"x+=+%281%2F%284p%29%29y%5E2\"   DISABLED_style= \"max-width:90%; height:auto;\" ><br><BR>\n" );
document.write( "where p is the distance from the vertex to the focus.<br><BR>\n" );
document.write( "In your example, the equation in that form is<br><BR>\n" );
document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=x+=+%281%2F16%29y%5E2 ALIGN=MIDDLE  ALT=\"x+=+%281%2F16%29y%5E2\"   DISABLED_style= \"max-width:90%; height:auto;\" ><br><BR>\n" );
document.write( "which means p=4 and the focus is at (4,0).<br><BR>\n" );
document.write( "Then, since this focal chord cuts the parabola at (4,8), the focal chord is a vertical line passing through (4,0) and (4,8); so the equation of the focal chord is x=4. </SPAN>\n" );
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