document.write( "Question 620450: The filament of a light bulb is a thin wire that glows when electricity passes through it. The filament of a car headlight is at the focus of a parabolic reflector, which sends light out in a straight beam. Given that the filament is 2 inches from the vertex, find an equation for the cross-section of the reflector. If the reflector 6 inches wide, how deep is it?
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Algebra.Com's Answer #390133 by nerdybill(7384)\"\" \"About 
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The filament of a light bulb is a thin wire that glows when electricity passes through it. The filament of a car headlight is at the focus of a parabolic reflector, which sends light out in a straight beam. Given that the filament is 2 inches from the vertex, find an equation for the cross-section of the reflector. If the reflector 6 inches wide, how deep is it?
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\n" ); document.write( "Horizontal parabola has the form:
\n" ); document.write( "x = 1/(4c)(y-k)^2 + h
\n" ); document.write( "Since the focus is 2 inches from the vertex
\n" ); document.write( "c = 2
\n" ); document.write( "and, we can assume the vertex is at (0,0)
\n" ); document.write( "x = 1/(4*2)(y-0)^2 + 0
\n" ); document.write( "x = 1/8y^2 (equation for the cross-section)
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\n" ); document.write( "if the reflector is 6 inches wide then
\n" ); document.write( "y = 3
\n" ); document.write( "x = 1/8y^2
\n" ); document.write( "x = 1/8(3)^2
\n" ); document.write( "x = 1/8(9)
\n" ); document.write( "x = 9/8 inches
\n" ); document.write( "or
\n" ); document.write( "x = 1 and 1/8 inches deep\r
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