y′=4x-1/x^2+9/x^3
具体是：y′=(2x^2)′＋(1/x)′-(3/x^3)′
=4x+(1′x－1x′)/x^2－[3′x^3－3×(x^3)′]/(x^3)^2
=4x－1/x^2+9/x^3