lim (1+2+……n)/(n+2)-n/2 n→无限

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lim (1+2+……n)/(n+2)-n/2 n→无限
lim (1+2+……n)/(n+2)-n/2 n→无限

lim (1+2+……n)/(n+2)-n/2 n→无限
lim(n-> ∞)[(1+2+...+n)/(n+2)- n/2]
=lim(n-> ∞)[n(n+1)/[2(n+2)]- n/2]
=lim(n-> ∞)[n(n+1)-n(n+2) ]/[2(n+2)]
=lim(n-> ∞)-n/[2(n+2)]
=lim(n-> ∞)-1/[2(1+2/n)]
=-1/2

1+2+……n=(1+n)*n/2
lim (1+2+……n)/(n+2)-n/2=lim-n/(2n+4)=-1/2