第2个回答 2019-10-04
(8)
lim(x->∞) (2x-1)^20.(x-1)^10/(2x+1)^30
分子分母同时除以 x^30
=lim(x->∞) (2-1/x)^20. (1-1/x)^10/(2+1/x)^30
= 2^20 /2^30
=1/1024
(10)
x->∞ , 2x/(x^2+1) ->0
cos[2x/(x^2+1) ] ~ 1 - (1/2) [2x/(x^2+1) ]^2
lim(x->∞) xcos[2x/(x^2+1) ]
=lim(x->∞) x { 1 - (1/2) [2x/(x^2+1) ]^2 }
=(1/2) lim(x->∞) x [ 2(x^2+1)^2 - 4x^2 ]/(x^2+1) ]^2
=(1/2) lim(x->∞) x ( 2x^4 +2 )/(x^2+1)^2
发散