document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=586673>Question 586673</A>: <I><SPAN STYLE=\"word-break: break-all;\"> a focus on an ellipse is at origin.the directrix is the line x=4 and the eccentricity is 1/2.then the length of the semi major axis is </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #373930 by </B><A HREF=/tutors/aboutme.mpl?userid=lwsshak3><B>lwsshak3(11628)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=lwsshak3><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/images/nopicture.jpg><BR>You can <A HREF=\"/cgi-bin/embed-solution.mpl?show=1&solution=373930\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> a focus on an ellipse is at origin.the directrix is the line x=4 and the eccentricity is 1/2.then the length of the semi major axis is<BR>\n" );
document.write( "**<BR>\n" );
document.write( "x=a/e=4<BR>\n" );
document.write( "a=4e=4*(1/2)=2<BR>\n" );
document.write( "a^2=4<BR>\n" );
document.write( "..<BR>\n" );
document.write( "e=c/a<BR>\n" );
document.write( "c=a*e=2*(1/2)=1<BR>\n" );
document.write( "c^2=1<BR>\n" );
document.write( "..<BR>\n" );
document.write( "center: (-1,0)<BR>\n" );
document.write( "c^2=a^2-b^2<BR>\n" );
document.write( "b^2=a^2-c^2=4-1=3<BR>\n" );
document.write( "b=&#8730;3<BR>\n" );
document.write( "length of semi major axis=2&#8730;3<BR>\n" );
document.write( "..<BR>\n" );
document.write( "Equation of ellipse:<BR>\n" );
document.write( "(x+1)^2/4+y^2/3=1 </SPAN>\n" );
document.write( "</TD></TR></TABLE>\n" );