document.write( "Question 1187647: find the equation of a parabola with vertex on the line y=2x, axis parallel to the x-axis and passing through (3/2, 1) and (3,4).\r
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Algebra.Com's Answer #818689 by greenestamps(13200)\"\" \"About 
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\n" ); document.write( "The given information is unusual, so initially we don't have a good idea of where to go with the problem. So we do the only thing we can -- write the general form of the equation and use each the two given points in that equation to see what it gives us.

\n" ); document.write( "The vertex is on the line y=2x, so we can call the coordinates of the vertex (a,2a). Then the vertex form of the equation of a parabola parallel to the x-axis with vertex (a,2a) is

\n" ); document.write( "\"%28x-a%29+=+%281%2F%284p%29%29%28y-2a%29%5E2\"

\n" ); document.write( "Plug in (x,y)=(1.5,1) and (x,y)=(3,4) to get two equations in a and p:

\n" ); document.write( "\"1.5-a=%281%2F%284p%29%29%281-2a%29%5E2\"

\n" ); document.write( "\"4p%281.5-a%29=1-4a%2B4a%5E2\" [1]

\n" ); document.write( "\"3-a=%281%2F%284p%29%29%284-2a%29%5E2\"

\n" ); document.write( "\"4p%283-a%29=16-16a%2B4a%5E2\" [2]

\n" ); document.write( "Subtract [1] from [2]:

\n" ); document.write( "\"4p%281.5%29=15-12a\"
\n" ); document.write( "\"6p=15-12a\"
\n" ); document.write( "\"p=2.5-2a\"
\n" ); document.write( "\"4p=10-8a\" [3]

\n" ); document.write( "Substitute [3] in [2]:

\n" ); document.write( "\"%2810-8a%29%283-a%29=16-16a%2B4a%5E2\"
\n" ); document.write( "\"30-34a%2B8a%5E2=16-16a%2B4a%5E2\"
\n" ); document.write( "\"4a%5E2-18a%2B14=0\"
\n" ); document.write( "\"2a%5E2-9a%2B7=0\"
\n" ); document.write( "\"%282a-7%29%28a-1%29=0\"

\n" ); document.write( "\"a=3.5\" or \"a=1\"

\n" ); document.write( "There will be two parabolas that satisfy the given conditions.

\n" ); document.write( "(1) a=3.5; 4p=10-8a=-18; 2a=7

\n" ); document.write( "\"x-3.5=%28-1%2F18%29%28y-7%29%5E2\"

\n" ); document.write( "(2) a=1; 4p=10-8a=2; 2a=2

\n" ); document.write( "\"x-1=%281%2F2%29%28y-2%29%5E2\"

\n" ); document.write( "Here is a graph of the two parabolas, one with vertex (1,2) and the other with vertex (3.5,7) and both passing through the points (1.5,1) and (3,4)

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