2x3+3x2+5 例4求lm (—型) x→)∞7x3+4x2-1 解先用x3去除分子分母,分出无穷小,再求极限 35 2x3+3x2+5 2++ lim 2.3 2 Im x→0 7x+4x2-1 x→0 7+ 7 当a0≠0,b0≠0,m和n为非负整数时有 当n=m x+a1x+…+a lim x→b2x+b1x-1+…+bn 0,当n>m, 当 n< m Economic-mathematics 16-6 Wednesday, February 24, 2021Economic-mathematics 16 - 6 Wednesday, February 24, 2021 例4 . 7 4 1 2 3 5 lim 3 2 3 2 + − + + → x x x x x 求 解 ( 型 )   , , . 先用x 3去除分子分母 分出无穷小 再求极限 3 3 3 2 3 2 4 1 7 3 5 2 lim 7 4 1 2 3 5 lim x x x x x x x x x x + − + + = + − + + → → . 7 2 = 当a0  0,b0  0,m和n为非负整数时有      = + + + + + + − − → n n n m m m x b x b x b a x a x a   1 0 1 1 0 1 lim , , 0 0 n m b a 当 = 0,当n  m, ,当n  m