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

Toán Lớp 6: :Tìm x sao cho : (x +9) (2 -x) > 0

Toán Lớp 6: :Tìm x sao cho :
(x +9) (2 -x) > 0

Comments ( 2 )

  1. (x+9)(2-x)>0
    <=>\(\left[ \begin{array}{l}\begin{cases}x+9>0\\2-x>0\end{cases}\\\begin{cases}x+9<0\\2-x<0\end{cases}\end{array} \right.\) 
    <=>\(\left[ \begin{array}{l}\begin{cases}x>-9\\x>2\end{cases}\\\begin{cases}x<-9\\x<2\end{cases}\end{array} \right.\) 
    <=>\(\left[ \begin{array}{l}-9<x<2\\x\in∅\end{array} \right.\) 
    <=> -9<x<2
    Vậy S={x|-9<x<2}

  2. Giải đáp:
    $-9<x<2$
    Lời giải và giải thích chi tiết:
    $(x +9) (2 -x) > 0$
    ⇔\(\left[ \begin{array}{l}x+9>0\\2-x>0\end{array} \right.\) hay \(\left[ \begin{array}{l}x+9<0\\2-x<0\end{array} \right.\)
    ⇔\(\left[ \begin{array}{l}x>-9\\-x>-2\end{array} \right.\)  hay \(\left[ \begin{array}{l}x<-9\\-x<-2\end{array} \right.\)
    ⇔\(\left[ \begin{array}{l}x>-9\\x<2\end{array} \right.\) hay \(\left[ \begin{array}{l}x<-9\\x>-2\end{array} \right.\)
    ⇔$-9<x<2$

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