当x→0时,ex—为x的三阶无穷小,则a=________,b=________·

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问题 当x→0时,ex为x的三阶无穷小,则a=________,b=________·

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答案[*]

解析 ex=1+x++o(x3),
=1-bx+b2x2-b3x3+o(x3)得
=(1+ax)[1-bx+b2x2-b3x3+o(x3)]
=1+(a-b)x+(b2-ab)x2+(ab2-b3)x3+o(x3),
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