f'(x)=(x-1)(x-2)...(x-100)+x(x-2)....(x-100)+x(x-1)(x-3)...(x-100)+...
后面各项依次少一个因式,但都有x
所以f'(x)=(-1)*(-2)*....*(-100)+0 (因都有x,乘积为0)
=1*2*......*100
=100! (100的阶乘)
f'(x)=x'*(x-1)(x-2)……(x-100)+x*(x-1)'*(x-2)*……(x-100)+……+x(x-1)9x-2)……(x-99)*(x-100)'
除了第一项,后面都有x这一项的,所以x=0时都等于0
所以f'(0)=1*(0-1)(0-2)……(0-100)=100!
用导数的定义求
f’(0)=limf(x)-f(0)/x-0=lim(x-1)(x-2)…(x-100)=100!
x-0 x-0