document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=1126329>Question 1126329</A>: <I><SPAN STYLE=\"word-break: break-all;\"> a large reflecting telescope has a parabolic mirror that s 4 m eters in diamter and 25 centimeter deep. it requires a cage for the observer with an eyepiece at the focus of the mirror how far up the tube of the telescope must the cage be built? this design is called a prime focus telescope. </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #742671 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=742671\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> a large reflecting telescope has a parabolic mirror that s 4 meters in diameter and 25 centimeter deep. it requires a cage for the observer with an eyepiece at the focus of the mirror how far up the tube of the telescope must the cage be built?<BR>\n" );
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document.write( "Make the parabola symmetric about the y-axis with its vertex at (0,-25)<BR>\n" );
document.write( "--> 3 points: (-200,0), (0,-25) and (200,0)<BR>\n" );
document.write( "Find an equation for the parabola.<BR>\n" );
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document.write( "ax^2 + bx + c = y<BR>\n" );
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document.write( "(0,-25) --> c = -25 <BR>\n" );
document.write( "(-200,0) --> 40000a -200b -25 = 0<BR>\n" );
document.write( "(+200,0) --> 40000a +200b -25 = 0<BR>\n" );
document.write( "---------------------------------------- Subtract<BR>\n" );
document.write( "--> b = 0<BR>\n" );
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document.write( "a = 25/40000 = 1/1600<BR>\n" );
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document.write( "y = x^2/1600 - 25 is the parabola<BR>\n" );
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document.write( "There are several ways to find the focus.<BR>\n" );
document.write( "Can you do the rest?\r<BR>\n" );
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