作者LuisSantos (^______^)
看板trans_math
标题Re: [积分] 今年师大考题
时间Mon Jul 9 13:20:10 2007
※ 引述《dora963 (.........)》之铭言：
: 不知道题目有没有记错...
: 记错请指正@@
: ｌｉｍ √￣￣￣
: x→∞ x+4x^2 -2x
: 请问要怎麽做&答案是多少呢@@??
lim √(x + (4)(x^2)) - 2x
x→∞
(√(x + (4)(x^2)) - 2x)(√(x + (4)(x^2)) + 2x)
= lim ------------------------------------------------
x→∞ √(x + (4)(x^2)) + 2x
(x + (4)(x^2)) - (4)(x^2)
= lim ----------------------------
x→∞ √(x + (4)(x^2)) + 2x
x
= lim -----------------------
x→∞ √(x + (4)(x^2)) + 2x
1
= lim --------------------
x→∞ √((1/x) + 4) + 2
1
= ---------------
√(0 + 4) + 2
1 1
= ------- = ---
2 + 2 4
--
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