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Summer Clouds

15/06/2017 at 17:02
Answers
3
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Solve the equation: \(\left|x+2\right|=2x-1\)

 




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  • ...
    Phan Thanh Tinh Coordinator 15/06/2017 at 19:18

    Condition :\(\left|x+2\right|\ge0\Rightarrow2x-1\ge0\Rightarrow x\ge\dfrac{1}{2}\)

    1st case : \(x+2\ge0\Leftrightarrow x\ge-2\),then :

    \(x+2=2x-1\Leftrightarrow2x-x=2+1\Leftrightarrow x=3\) (satisfied)

    2nd case : \(x+2< 0\Leftrightarrow x< -2\),then :

    \(-x-2=2x-1\Leftrightarrow2x+x=-2+1\Leftrightarrow3x=-1\Leftrightarrow x=-\dfrac{1}{3}\)

                                                                                                    (absurd)

    Summer Clouds selected this answer.
  • ...
    Phan Thanh Tinh Coordinator 15/06/2017 at 19:19

    Tran Kim Anh,you copied my style,right ?

  • ...
    Tran Kim Anh 15/06/2017 at 18:35

    We have |x+2| = 2x -1 \(\Rightarrow\) 2x - 1 \(\ge\) 0 \(\Rightarrow\) x \(\ge\)\(\dfrac{1}{2}\)

    1\(^{st}\)case: x \(\ge\) 0 \(\Rightarrow\)|x+2| = x+2 \(\Rightarrow\)x + 2 = 2x -1 \(\Rightarrow\)  x = 3 (satisfied)

    2\(^{nd}\)case: x < 0 \(\Rightarrow\) |x+2| = - (x+2) \(\Rightarrow\)-x -2 = 2x - 1\(\Rightarrow\)x = \(\dfrac{-1}{3}\)(absurd)

    Hence, x = 3.


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