document.write( "Question 1108707: A parabola has a focus of F(-1,5) and a directrix of y=6.\r
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Algebra.Com's Answer #723749 by Edwin McCravy(20060)\"\" \"About 
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document.write( "We must graph it and know some facts about the graph \r\n" );
document.write( "and the equation of a parabola.\r\n" );
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document.write( "We plot the focus (a point) and the directrix (a line) in green:\r\n" );
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document.write( "We draw a line from the focus perpendicular to the directrix,\r\n" );
document.write( "and find the midpoint.\r\n" );
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document.write( "The midpoint of that line is the vertex of the parabola.\r\n" );
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document.write( "We can tell from the graph that the vertex is (-1,5.5),\r\n" );
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document.write( "\"5.5=5%261%2F2=11%2F2\" the vertex is \"%28matrix%281%2C3%2C-1%2C%22%2C%22%2C11%2F2%29%29\"\r\n" );
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document.write( "Next draw two squares, one on each side of that line, with\r\n" );
document.write( "that line as their common side:\r\n" );
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document.write( "Skwtch the parabola through the vertex and the left and right\r\n" );
document.write( "bottom corners of those two squares:\r\n" );
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document.write( "The equation of a parabola that opens vertically is\r\n" );
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document.write( "\"matrix%281%2C3%2C%0D%0A%0D%0A%28x-h%29%5E2%2C%22%22=%22%22%2C%22%22+%2B-+4p%28y-k%29%29\"\r\n" );
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document.write( "Where the vertex is (h,k) = \"%28matrix%281%2C3%2C-1%2C%22%2C%22%2C11%2F2%29%29\"\r\n" );
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document.write( "and p is the positive distance from the vertex to the focus, \r\n" );
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document.write( "so \"matrix%281%2C3%2Cp%2C%22%22=%22%22%2C1%2F2%29\"\r\n" );
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document.write( "and if the parabola opens positive the sign is taken + and if \r\n" );
document.write( "the parabola opens downward the sign is taken negative.  \r\n" );
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document.write( "This parabola opens downward, so we use the - sign.\r\n" );
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document.write( "So the equation is:\r\n" );
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document.write( "which simplifies to:\r\n" );
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document.write( "\"matrix%281%2C3%2C%0D%0A%0D%0A%28x%2B1%29%5E2%2C%22%22=%22%22%2C%22%22+-2%28y-11%2F2%29%29\"\r\n" );
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document.write( "Edwin
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