document.write( "Question 1102379: Find an equation for the ellipse with center
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\n" ); document.write( "\n" ); document.write( "Find an equation for the ellipse with center
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Algebra.Com's Answer #717072 by KMST(5328)\"\" \"About 
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An ellipse with foci (3, ±2)
\n" ); document.write( "must have a center midway between the foci, at (3,0),
\n" ); document.write( "and its focal distance must be \"c=2\" ,
\n" ); document.write( "the distance between center and either focus.
\n" ); document.write( "It also must have a major axis on the line x=3,
\n" ); document.write( "where the foci and center are located.
\n" ); document.write( "If the length of the major axis is 6,
\n" ); document.write( "the semi-major axis is \"a=6%2F2=3\" ,
\n" ); document.write( "and that tells us the vertices are 3 units above and below the center,
\n" ); document.write( "at (3,-3) and (3,3).
\n" ); document.write( "In an ellipse, the semi-minor axis \"b\" is related to \"a\" and \"c\" by
\n" ); document.write( "\"b%5E2%2Bc%5E2=a%5E2\" , so
\n" ); document.write( "\"b%5E2%2B2%5E2=3%5E2\" ,
\n" ); document.write( "\"b%5E2%2B4=9\" ,
\n" ); document.write( "\"b%5E2=9-4\" ,
\n" ); document.write( "\"b%5E2=5\" .
\n" ); document.write( "The equation for an ellipse where center, foci, and vertices differ only on the y-coordinate is
\n" ); document.write( "\"%28x-h%29%5E2%2Fb%5E2%2B%28y-k%29%5E2%2Fa%5E2=1\" , where (h,k) is the center.
\n" ); document.write( "Substituting the values we now know for \"a\", \"b%5E2\" , \"h\" and \"k\" , we get
\n" ); document.write( "\"highlight%28%28x-3%29%5E2%2F5%2By%5E2%2F9=1%29\" ,
\n" ); document.write( "and the ellipse, wit its foci looks like this
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\n" ); document.write( "The equation for an ellipse with foci at (3, ±4) and major axis 10
\n" ); document.write( "can be found the same way.
\n" ); document.write( "\"c=4\" , \"a=10%2F2=5\" .
\n" ); document.write( "As \"4%7D%7D+and+%7B%7B%7B5\" are leg and hypotenuse of a 3-4-5 right triangle,
\n" ); document.write( "\"b=3\" and \"b%5E2=9\" .
\n" ); document.write( "The equation is \"highlight%28%28x-3%29%5E2%2F9%2By%5E2%2F25=1%29\" .
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