HOW TO DO THIS?

回答 (1)

螞蟻雄兵

2011-06-27 3:31 am

✔ 最佳答案

lim(x->－∞)_[√(4x^2－x)+2x]
=lim(x->－∞)_｛√[4x^2－2*(2x)*(1/4)]+2x｝
=lim(x->－∞)_｛√[4x^2－2*(2x)*(1/4)+(1/16)]+2x｝
=lim(x->－∞)_[｜2x－1/4｜+2x]
=lim(x->－∞)_(－2x+1/4+2x)
=1/4

or
lim(x->－∞)_[√(4x^2－x)+2x]
=lim(x->－∞)_｛[√(4x^2－x)+2x]*[√(4x^2－x)－2x]｝/[√(4x^2－x)－2x]
=lim(x->－∞)_[(4x^2－x)－4x^2]/[√(4x^2－x)－2x]
=lim(x->－∞)_－x/[√(4x^2－x)－2x]
=lim(x->－∞)_1/[√(4+1/x)+2]
=1/4

2011-06-27 09:59:05 補充：
除以(－x)..............

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