数学极限题2道1,lim= [2^n+(a-1)^(n+1)] / [2^(n+1)+(a-1)^n] =1/2 ,则a范围2,lim=[3r^n] / [1+r^(n+1)]=t>1,则r范围

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数学极限题2道1,lim= [2^n+(a-1)^(n+1)] / [2^(n+1)+(a-1)^n] =1/2 ,则a范围2,lim=[3r^n] / [1+r^(n+1)]=t>1,则r范围
数学极限题2道
1,lim= [2^n+(a-1)^(n+1)] / [2^(n+1)+(a-1)^n] =1/2 ,则a范围
2,lim=[3r^n] / [1+r^(n+1)]=t>1,则r范围

数学极限题2道1,lim= [2^n+(a-1)^(n+1)] / [2^(n+1)+(a-1)^n] =1/2 ,则a范围2,lim=[3r^n] / [1+r^(n+1)]=t>1,则r范围
1.分子分母同除于2^n得
lim [2^n+(a-1)^(n+1)] / [2^(n+1)+(a-1)^n]
=lim {1+(a-1)[(a-1)/2]^n}÷{2+[(a-1)/2]^n}
=1/2
从而可知要求lim [(a-1)/2]^n=0,即要求 |(a-1)/2|