By making the substitution u-(sin)^(-1) (x/3), simplify: x^2/√(9-x^2 )
[3 sin(u)]^2 / sqrt(9 - [3 sin(u)]^2)
[ 9 sin^2(u) ] / sqrt(9 - 9 sin^2(u))
[ 9 sin^2(u) ] / sqrt(9{1 - sin^2(u)})
[ 9 sin^2(u) ] / sqrt(9cos^2(u))
[ 9 sin^2(u) ] / [3 cos(u)]
[ 3 sin^2(u) ] / [ cos(u)]
3 tan(u) sin(u)
YEa?