document.write( "Question 1081914: The focus of a parabola is (3,−7) and the directrix is y=−4.\r
\n" ); document.write( "\n" ); document.write( " \r
\n" ); document.write( "\n" ); document.write( "What is an equation of the parabola?\r
\n" ); document.write( "\n" ); document.write( " (x−3)2=−6(y+5.5)
\n" ); document.write( " (x−3)2=−3(y+10)
\n" ); document.write( " (x−3)2=−12(y+10)
\n" ); document.write( " (x−3)2=−1.5(y+5.5) \n" ); document.write( "
Algebra.Com's Answer #695961 by Boreal(15235)\"\" \"About 
You can put this solution on YOUR website!
The coordinates of the focus are (h, k + (1/4a)), where h=3, and k+(1/4a)=-7
\n" ); document.write( "k+(1/4a)=-7
\n" ); document.write( "The vertex is half way between the focus and the directrix, or at (3, -5.5), so k=-5.5
\n" ); document.write( "-5.5+(1/4a)=-7
\n" ); document.write( "(1/4a)=-1.5
\n" ); document.write( "1=-6a
\n" ); document.write( "a=(-1/6)
\n" ); document.write( "The equation is y=(-1/6)(x-3)^2-5.5
\n" ); document.write( "or (y+5.5)=(-1/6)(x-3)^2
\n" ); document.write( "or -6(y+5.5)=(x-3)^2\r
\n" ); document.write( "\n" ); document.write( " \n" ); document.write( "
\n" );