(1+2分之1)乘(1-2分之1).用简便方法算

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  • 题目是:找规律 (1+2分之1)乘(1-2分之1)乘(1+3分之一)乘(1-3分之1)乘.乘(1+99分之1)乘(1-99分之1)吧

    先找规律吧

    (1+1/2)*(1-1/2)*(1+1/3)*(1-1/3)=3/4 * 8/9=2/3

    (1+1/2)*(1-1/2)*(1+1/3)*(1-1/3)*(1+1/4)*(1-1/4)=2/3 * 15/16=5/8=2.5/4

    (1+1/2)*(1-1/2)*(1+1/3)*(1-1/3)*.*(1+1/5)*(1-1/5)=5/8 * 24/25=3/5

    (1+1/2)*(1-1/2)*(1+1/3)*(1-1/3)*.*(1+1/6)*(1-1/6)=3/5 * 35/36=7/12=3.5/6

    由以上规律可以发现,

    (1+1/2)*(1-1/2)*(1+1/3)*(1-1/3)*.(1+1/n)*(1-1/n)

    =(n/2+0.5)/n

    所以:(1+1/2)*(1-1/2)*(1+1/3)*(1-1/3)*.*(1+1/99)*(1-1/99)

    =(99/2+0.5)/99 =50/99