limf (x) 0, ? ??? ?? ????,?? x 3 x 3 x 3 x x 3 limf (x) lim limx 3. x 3 ?? ?????? ????④ 2.函数极限的运算法则若那么=______; =______; =_________. 特别地, =_________(C 为常数). 0 0 x x x x limf (x) a, limg(x) b, ? ?? ? 0 x x (1) lim f (x) g(x) ??[] a±b 0 x x (2) lim f (x) g(x) ??[] a·b 0 x x f (x) (3) lim g(x) ? 0 x x lim Cf (x) ?[] 0 x x Climf (x) ?a (b 0) b ?【即时应用】(1) 思考:若函数 f(x) 、g(x) 满足那么是否正确? 提示: 不一定.如f(x)=x+ g(x)=x, 满足都不存在. x lim f (x) g(x) 0 ??[-]=, x x limf (x) limg(x) ?? ??=,1,x x lim f (x) g(x) 0, ??? ?[] x x limf (x) limg(x) ?? ??但和(2) 计算: =______. 【解析】答案: 2 2 x 1 x 1 lim x 1 ????? 2 x 1 x 1 x 1 lim lim x 1 2. x 1 ? ??? ???
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