Bạn tham khảo!
Giai
$TH_{1}$ : Xét $x$ $+$ $\dfrac{2}{5}$ $≥$ $0$
$⇔$ $x$ $≥$ $\dfrac{-2}{5}$
Ta có : $|$ $x$ $+$ $\dfrac{2}{5}$ $|$ $=$ $2x$
$⇔$ $x$ $+$ $\dfrac{2}{5}$ $=$ $2x$
$⇔$ $\dfrac{2}{5}$ $=$ $2x$ $-$ $x$
Vậy $\dfrac{2}{5}$ $=$ $x$ (Nhận vì $x$ $=$ $\dfrac{2}{5}$ $>$ $\dfrac{-2}{5}$)
$TH_{2}$ : Xét $x$ $+$ $\dfrac{2}{5}$ $<$ $0$|
$⇔$ $x$ $<$ $\dfrac{-2}{5}$
Ta có : $|$ $x$ $+$ $\dfrac{2}{5}$ $|$ $=$ $2x$
$⇔$ $-x$ $-$ $\dfrac{2}{5}$ $=$ $2x$
$⇔$ $-x$ $-$ $2x$ $=$ $\dfrac{2}{5}$
$⇔$ $-3x$ $=$ $\dfrac{2}{5}$
$⇔$ $x$ $=$ $\dfrac{-2}{15}$ (Loại vì $x$ $=$ $\dfrac{-2}{15}$ $>$ $\dfrac{-2}{5}$)
Từ 2 TH trên $⇔$ $x$ $=$ $\dfrac{2}{5}$
$FbBinhne2k88$
