设数列{an}满足an+1n=ann+1+1n(n+1).\text{设数列}\left\{a_n\right\}\text{满足}\frac{a_{n+1}}{n}=\frac{a_n}{n+1}+\frac{1}{n(n+1)}.
证明:{nan} 为等差数列;\text{证明:}\quad\{na_n\}\text{ 为等差数列;}
设f(x)=a1x+a2x2+⋯+amxm,求f′(2).\text{设}f(x)=a_{1}x+a_{2}x^{2}+\cdots+a_{m}x^{m},\text{求}f^{\prime}(2).
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