求导的数学题
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法一,f(x)=x(x-1)(x-2)(x-3)(x-4).(x-100)
设g(x) = (x-1)(x-2)(x-3)(x-4).(x-100)
那么f(x) = x*g(x)
f'(x) = x * g'(x) + g(x)
所以f'(0) = g(0) = 100!
法二f(x)=x(x-1)(x-2)……(x-100)两边取对数得lnf(x)=lnx+ln(x-1)+ln(x-2)+……+ln(x-1)
两边求导数得f'(x)/f(x)=1/x+1/(x-1)+1/(x-2)+……+1/(x-100)
所以f'(x)=f(x)[1/x+1/(x-1)+1/(x-2)+……+1/(x-100)……(*)
=(x-1)(x-2)……(x-100)+x(x-2)……(x-100)+x(x-1)……(x-100)+……+x(x-1)(x-2)……(x-99)
f'(0)=1*2*3*4……*100=100!
设g(x) = (x-1)(x-2)(x-3)(x-4).(x-100)
那么f(x) = x*g(x)
f'(x) = x * g'(x) + g(x)
所以f'(0) = g(0) = 100!
法二f(x)=x(x-1)(x-2)……(x-100)两边取对数得lnf(x)=lnx+ln(x-1)+ln(x-2)+……+ln(x-1)
两边求导数得f'(x)/f(x)=1/x+1/(x-1)+1/(x-2)+……+1/(x-100)
所以f'(x)=f(x)[1/x+1/(x-1)+1/(x-2)+……+1/(x-100)……(*)
=(x-1)(x-2)……(x-100)+x(x-2)……(x-100)+x(x-1)……(x-100)+……+x(x-1)(x-2)……(x-99)
f'(0)=1*2*3*4……*100=100!
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