F(x)=x(x-1)(x-2)...(x-19)(x-20)Найти f'(0)

Обозначим [latex]h(x)=(x-1)(x-2)...(x-19)(x-20)[/latex] [latex]f(x)=x*h(x)[/latex] [latex]f'(x)=(x*h(x))=(x)'*h(x)+x*h'(x)=\\\\1*h(x)+x*h'(x)=h(x)+x*h'(x)[/latex] [latex]f'(0)=h(0)+0*h'(x)=h(0)[/latex] [latex]f'(0)=h(0)=(0-1)(0-2)*...*(0-19)*(0-20)=\\\\(-1)*(-2)*(-3)*...*(-19)*(-20)=\\\\1*2*3*..*19*20=20!=2432902008176640000[/latex]