document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=768162>Question 768162</A>: <I><SPAN STYLE=\"word-break: break-all;\"> A parabolic arch has a height of 20 m and a width of 36 m at the base.  If the vertex of the parabola is at the top of the arch, at which height above the base is it 18 m wide? </SPAN>\n" );
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document.write( "Representing the arch, draw a parabola that opens downward with the the vertex at (0,20).<BR>\n" );
document.write( "Standard form of equation: y=A(x-h)^2+k, (h,k)=(x,y) coordinates of the vertex<BR>\n" );
document.write( "y=A(x-0)^2+20<BR>\n" );
document.write( "y=Ax^2+20<BR>\n" );
document.write( "Using coordinates of right side of the base(18,0)to find A<BR>\n" );
document.write( "0=A(18^2)+20<BR>\n" );
document.write( "-20=324A<BR>\n" );
document.write( "A=-20/324=-5/81<BR>\n" );
document.write( "When arch is 18m wide, x=9<BR>\n" );
document.write( "y=(-5/81)(9^2)+20=15m<BR>\n" );
document.write( "height above the base when arch is 18 m wide=15m </SPAN>\n" );
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