y=(x-1)(x-2)²(x-3)³(x-4)^4令g(x)=(x-2)²(x-3)³(x-4)^4y=(x-1)g(x)y'=(x-1)'g(x)+g(x)'(x-1)y'=g(x)+g(x)'(x-1)y'(1)=g(1)+g(1)'×0y'(1)=g(1)+0y'(1)=g(1)y'(1)=(-1)²(-2)³(-3)^4y'(1)=-648
最后是x-1
用定义做。f'(1)=lim(x->1)[f(x)-f(1)]/(x-1)=0
两边同取对数