document.write( "Question 415344: Find the equation for a parabola with its focus at (5,0) and with directrix x=-5\r
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Algebra.Com's Answer #291233 by Edwin McCravy(20060)\"\" \"About 
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Find the equation for a parabola with its focus at (5,0) and with
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document.write( "Here is its focus, the point F(5,0), and its directrix, the green\r\n" );
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document.write( "The vertex of a parabola is half-way between the focus point and the \r\n" );
document.write( "directrix line.  Looking at the graph, that puts the vertex at the origin\r\n" );
document.write( "V(0,0).  p is the distance from the vertex to the focus, taken as a positive\r\n" );
document.write( "number if the parabola is to open to the right and p is taken as a negative \r\n" );
document.write( "number if the parabola is to open to the left.\r\n" );
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document.write( "This one opens to the right, so p is taken positive as 5, the distance\r\n" );
document.write( "between the vertex and the focus, which is also half of the distance between\r\n" );
document.write( "the focus and the directrix.  So its equation is\r\n" );
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document.write( "(y - k)² = 4p(x - h)\r\n" );
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document.write( "and since the vertex is (h,k) = (0,0) and p = 5, that simplifies to\r\n" );
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document.write( "(y - 0)² = 4*5(x - 0)\r\n" );
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document.write( "      y² = 20x \r\n" );
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document.write( "That's the equation you wanted\r\n" );
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document.write( "To finish the graph we constract a square on each side of the line\r\n" );
document.write( "that goes from the focus through the vertex to the directrix, like this:\r\n" );
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document.write( "Then we can sketch in the parabola through the vertex and the right \r\n" );
document.write( "uppermost and lowermost corners of those two squares:\r\n" );
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document.write( "Edwin
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