A. a = 2,b = 8 B. a = 2,b = 5 C. a = 0,b = -8 D. a = 2,b = -8A. a = 2,b = 8 B

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问题

选项 A. a = 2,b = 8
B. a = 2,b = 5
C. a = 0,b = -8
D. a = 2,b = -8

答案D

解析正确答案是D。 提示:当x→2,分母极限为零,分子也必须为零,故有4 + 2a + b = 0;利用洛必达法则, 所以a=2,代入4 + 2a + b= 0有b=-8。
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