document.write( "Question 1206395: A cross section of a reflector of a television satellite dish is a parabola that measures 5 ft across with a depth of 2 ft. How far from the vertex should the receiving antenna be placed?\r
\n" ); document.write( "\n" ); document.write( "A. 0.3125 ft
\n" ); document.write( "B. 0.78125 ft
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\n" ); document.write( "F. 1.8125 ft \n" ); document.write( "

Algebra.Com's Answer #843835 by ikleyn(52855) $\"\"$ $\"About$

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\n" ); document.write( "A cross section of a reflector of a television satellite dish is a parabola
\n" ); document.write( "that measures 5 ft across with a depth of 2 ft. How far from the vertex should the receiving antenna be placed?
\n" ); document.write( "A. 0.3125 ft
\n" ); document.write( "B. 0.78125 ft
\n" ); document.write( "C. 0.2500 ft
\n" ); document.write( "D. 1.25 ft
\n" ); document.write( "E. 0.625 ft
\n" ); document.write( "F. 1.8125 ft
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document.write( "Place the origin of the coordinate system at vertex of the parabola.\r\n" );
document.write( "Use the vertex form equation of this parabola \r\n" );
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document.write( "    y = .        (1)\r\n" );
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document.write( "At x = 2.5 ft, we are given y = 2 ft.  So, this vertex equation takes the form\r\n" );
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document.write( "    2 = ,  which gives  a =  =  = .\r\n" );
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document.write( "So, equation (1) is  \r\n" );
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document.write( "    y = .    (2)\r\n" );
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document.write( "For the parabola with equation y = ,  the distance from the vertex to the focus is\r\n" );
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document.write( "    f = .\r\n" );
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document.write( "In our case, the distance from the vertex to the focus is    =  cm = 0.78125 ft.\r\n" );
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document.write( "ANSWER.  The distance from the vertex to the focus, where the filament should be placed, is 0.78125 ft.  \r\n" );
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document.write( "         Option (B).\r\n" );
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