document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=1140704>Question 1140704</A>: <I><SPAN STYLE=\"word-break: break-all;\"> I have no clue how to start off with this problem. Any help would be great.\r<BR>\n" );
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document.write( "Dish antennas have a parabolic cross-section. This concentrates signals onto a sensor at the focus of the parabola. A dish antenna is 1 meter wide and 20 centimeters deep. How far from the bottom of this dish should the sensor be positioned? </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #761242 by </B><A HREF=/tutors/aboutme.mpl?userid=greenestamps><B>greenestamps(13200)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=greenestamps><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=greenestamps><BR>You can <A HREF=\"/cgi-bin/embed-solution.mpl?show=1&solution=761242\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> <br><BR>\n" );
document.write( "There are two problems with the solution by tutor @josgarithmetic:<br><BR>\n" );
document.write( "(1) The \"1\" width is meters; the \"20\" depth is centimeters.  You need to use consistent units.  Changing the 1 meter to 100 centimeters, the second point on the parabola would be (100,20) instead of (1,20).<br><BR>\n" );
document.write( "(2) The 100 centimeters is the total width of the parabola; the second point on the parabola is only half that distance from the vertex.  The correct second point on the parabola is (50,20).<br><BR>\n" );
document.write( "So now<br><BR>\n" );
document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=y+=+%281%2F4p%29x%5E2 ALIGN=MIDDLE  ALT=\"y+=+%281%2F4p%29x%5E2\"   DISABLED_style= \"max-width:90%; height:auto;\" ><br><BR>\n" );
document.write( "where p is the distance from the vertex (bottom of the dish) to the focus the sensor).  Using the second point (50,20),<br><BR>\n" );
document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=20+=+%281%2F4p%29%2850%5E2%29 ALIGN=MIDDLE  ALT=\"20+=+%281%2F4p%29%2850%5E2%29\"   DISABLED_style= \"max-width:90%; height:auto;\" ><BR>\n" );
document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=1%2F4p+=+20%2F%2850%5E2%29+=+1%2F125 ALIGN=MIDDLE  ALT=\"1%2F4p+=+20%2F%2850%5E2%29+=+1%2F125\"   DISABLED_style= \"max-width:90%; height:auto;\" ><BR>\n" );
document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=p+=+125%2F4 ALIGN=MIDDLE  ALT=\"p+=+125%2F4\"   DISABLED_style= \"max-width:90%; height:auto;\" ><br><BR>\n" );
document.write( "ANSWER:  The sensor should be placed 125/4 = 31.25 cm from the bottom of the dish. </SPAN>\n" );
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