化简阶乘式子3/(1!+2!+3!)+4/(2!+3!+4!)+..+(n+2)/(n!+(n+1)!+(n+2)!)=?

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化简阶乘式子3/(1!+2!+3!)+4/(2!+3!+4!)+..+(n+2)/(n!+(n+1)!+(n+2)!)=?化简阶乘式子3/(1!+2!+3!)+4/(2!+3!+4!)+..+(n+2

化简阶乘式子3/(1!+2!+3!)+4/(2!+3!+4!)+..+(n+2)/(n!+(n+1)!+(n+2)!)=?
化简阶乘式子
3/(1!+2!+3!)+4/(2!+3!+4!)+..+(n+2)/(n!+(n+1)!+(n+2)!)=?

化简阶乘式子3/(1!+2!+3!)+4/(2!+3!+4!)+..+(n+2)/(n!+(n+1)!+(n+2)!)=?
原式=0.5×(1/1!+1/2!+.+1/n!)
=0.5(C1,1+C1,2+.+C1,n)
=0.5×(C2,n)
=n(n-1)/4