求证一列高数数列极限题:lim(3n^2+n)/(2n^2-1)=3/2
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求证一列高数数列极限题:lim(3n^2+n)/(2n^2-1)=3/2
用N-ε语言
对于任意ε>0
存在N=max(1,5/2ε)
当n>N时
|(3n^2+n)/(2n^2-1)-3/2|
=|(6n^2+2n-6n^2+3)/[2(2n^2-1)]|
=(2n+3)/[2(2n^2-1)]
因为n>N>=1,所以2n+32n^2-n^2=n^2
(分子更大,分母更小的数更大)
对于任意ε>0
存在N=max(1,5/2ε)
当n>N时
|(3n^2+n)/(2n^2-1)-3/2|
=|(6n^2+2n-6n^2+3)/[2(2n^2-1)]|
=(2n+3)/[2(2n^2-1)]
因为n>N>=1,所以2n+32n^2-n^2=n^2
(分子更大,分母更小的数更大)
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