The slope of tangent at any point \( (x,y) \) on a curve \( y=y(x) \) is \( \dfrac{x^2+y^2}{2xy} \), \( x>0 \). If \( y(2)=0 \), then a value of \( y(8) \) is:
\( -2\sqrt{3} \)
\( 2\sqrt{3} \)
\( -4\sqrt{2} \)
\( 4\sqrt{3} \)