document.write( "Question 854642: Find the equation of the ellipse described. Focus at (0, -3) and (0, 3) vertices at (0, 7) and (0, -7) \n" ); document.write( "
Algebra.Com's Answer #514835 by KMST(5328)\"\" \"About 
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With vertices at (0, 7) and (0, -7),
\n" ); document.write( "we know that the major axis is the vertical segment connecting (0, 7) and (0, -7),
\n" ); document.write( "and that the center of the ellipse is located at (0,0),
\n" ); document.write( "the midpoint of the major axis.
\n" ); document.write( "We also know that the semi-major axis will be
\n" ); document.write( "\"a=7\" , the distance from the center to either one of the vertices.
\n" ); document.write( "We know that the focal distance is
\n" ); document.write( "\"c=3\" , the distance from the center to the known focus.
\n" ); document.write( "We can find \"b\" , the semi-minor axis by using the known relation
\n" ); document.write( "\"a%5E2=b%5E2%2Bc%5E2\"
\n" ); document.write( "So \"7%5E2=b%5E2%2B3%5E2\"-->\"49=b%5E2%2B9\"-->\"49-9=b%5E2\"-->\"b%5E2=40\"
\n" ); document.write( "Since the equation of an ellipse centered at the origin, with a vertical major axis is
\n" ); document.write( "\"x%5E2%2Fb%5E2%2By%5E2%2Fa%5E2=1\"
\n" ); document.write( "Since \"b%5E2=40\" and \"a%5E2=7%5E2=49\" our equation is
\n" ); document.write( "\"highlight%28x%5E2%2F40%2By%5E2%2F49=1%29\"
\n" ); document.write( "
\n" ); document.write( " \"a%5E2=b%5E2%2Bc%5E2\" is Pythagoras applied to triangle \"red%28OBC%29\".
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