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222-9+11+12:2*14+14 = ? ( )

Toán Lớp 8: Tìm x |x|+|x+2|=3 b ) |x-5|=|x+2|

Tháng Hai 20, 2023 Toán học 1 Comment 0 views

Toán Lớp 8: Tìm x
|x|+|x+2|=3
b ) |x-5|=|x+2|

Comments ( 1 )

  1. maianhtuanh
    maianhtuanh
    20 Tháng Hai, 2023 at 8:58 sáng
    Reply
    a/ $\begin{array}{|c|cc|}\hline x&&-\infty&&-2&&0&&+\infty\\\hline x&&&-&|&-&0&+&\\\hline x+2&&&-&0&+&|&+\\\hline\end{array}$
    Xét khoảng $x<-2$
    $→-x-x-2=3\\↔-2x=5\\↔x=-\dfrac{5}{2}(TM)$
    Xét khoảng $-2\le x\le 0 $
    $\to -x+x+2=3\\↔2=3(vô\,\,lý)$
    $→$ Pt vô nghiệm trong khoảng $-2\le x\le 0$
    Xét khoảng $x>0$
    $→x+x+2=3\\↔2x=1\\↔x=\dfrac{1}{2}(TM)$
    Vậy $S=\{-\dfrac{5}{2};\dfrac{1}{2}\}$
    c/ $|x-5|=|x+2|\\↔\left[\begin{array}{1}x-5=x+2\\x-5=2-x\end{array}\right.\\↔\left[\begin{array}{1}0=7(vô\,\,lý)\\2x=7\end{array}\right.\\↔x=\dfrac{7}{2}$
    Vậy $S=\{\dfrac{7}{2}\}$
     

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