原题是:求x/((x-1)(x-2))的n阶导数.
设y=x/((x-1)(x-2))
y=2/(x-1)-1/(x-2)
y'=-2/(x-2)^2+1/(x-2)^2
y''=2*2/(x-2)^3-2/(x-2)^3=(-1)^2*2!(2/(x-2)^3-1/(x-1)^3)
y'''=-2*3!/(x-2)^4+3!/(x-2)^4=(-1)^3*3!(2/(x-2)^4-1/(x-1)^4)
...
y(n)=(-1)^n*n!(2/(x-2)^(n+1)-1/(x-1)^(n+1))
参考