I(x)=8k/x^2+k/(3-x)^2I'(x)=8k*x^(-2)+k*1/(3-x)^2=-2*8k*x(-3)+k*((x^2-6x+9)'-1'*(3-x)^2)/(3-x)^4=-16k/x^3+k*(2x-6)/(3-x)^4=-16k/x^3+2k/(3-x)^3若有不懂请追问