设Y=(2*4*6*8*...2n)/(1*3*5*7*...(2n-1)那么Y^2=[(2*4*6*8*...2n)/(1*3*5*7*...(2n-1))]^2而2^2>1*34^2>3*5.(2n)^2>(2n-1)(2n+1)于是分子>1*3^2*5^2*7^2*.*(2n+1)所以Y^2>2n+1Y>根号(2n+1)