Giúp mình với ạ mình cần gấp mai ktra rồi

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Giúp mình với ạ mình cần gấp mai ktra rồi
giup-minh-voi-a-minh-can-gap-mai-ktra-roi

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Đan Thu 5 years 2021-05-20T05:19:25+00:00 1 Answers 15 views 0

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  1. niczorrrr
    0
    2021-05-20T05:20:33+00:00
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    Bài 1:

    $\quad \lim\limits_{x\to 1}\dfrac{x^2 + ax + b}{x^2 -1} =\dfrac12$

    $\Leftrightarrow \lim\limits_{x\to 1}\dfrac{(x-1)(x +a + 1) + a + b + 1}{(x-1)(x+1)}=\dfrac12$

    $\Leftrightarrow \lim\limits_{x\to 1}\left(\dfrac{x+a+1}{x+1} + \dfrac{a+b+1}{x^2 -1}\right)= \dfrac12$

    $\Leftrightarrow \begin{cases}a + b+ 1=0\\\lim\limits_{x\to 1}\dfrac{x+a+1}{x+1}=\dfrac12\end{cases}$

    $\Leftrightarrow \begin{cases}a + b+ 1=0\\\dfrac{a+2}{2}=\dfrac12\end{cases}$

    $\Leftrightarrow \begin{cases}b = – a – 1\\a = -1\end{cases}$

    $\Leftrightarrow \begin{cases}a = -1\\b = 0\end{cases}$

    Vậy $(a;b)=(-1;0)$

    Bài 2:

    $\quad \lim\left(\sqrt{n^2 – n} – n\right)$

    $=\lim\dfrac{\left(\sqrt{n^2 – n} – n\right)\left(\sqrt{n^2 – n} + n\right)}{\sqrt{n^2 – n} +n}$

    $=\lim\dfrac{-n}{\sqrt{n^2 – n} +n}$

    $=\lim\dfrac{-1}{\sqrt{1 -\dfrac1n} +1}$

    $=\dfrac{-1}{\sqrt{1 – 0} +1}$

    $= -\dfrac12$

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Giải phương trình 1 ẩn: x + 2 - 2(x + 1) = -x . Hỏi x = ? ( )