Tìm x theo 2 cách : a) 2/5 – | x + 1 | = 3/4 B) | x – 1/3 | = 2/3 C) 4 | x – 1/2 | = 1/3

a) \(\dfrac{2}{5} – | x + 1 | = \dfrac{3}{4}\)

TH1: \(x+1<0\Leftrightarrow x< -1\)

pt \(\Rightarrow \dfrac{2}{5}-[-(x+1)]=\dfrac{3}{4}\)

\(\Rightarrow \dfrac{2}{5}+x+1=\dfrac{3}{4}\)

\(\Rightarrow x+\left({\dfrac{2}{5}+1}\right)=\dfrac{3}{4}\)

\(\Rightarrow x+\dfrac{2+5}{5}=\dfrac{3}{4}\)

\(\Rightarrow x+\dfrac{7}{5}=\dfrac{3}{4}\)

\(\Rightarrow x=\dfrac{3}{4}-\dfrac{7}{5}\)

\(\Rightarrow x=\dfrac{3.5-7.4}{20}\)

\(\Rightarrow x=\dfrac{-13}{20}\) (loại).

TH2: \(x+1\ge0\Leftrightarrow x\ge -1\)

pt \(\Rightarrow \dfrac{2}{5}-(x+1)=\dfrac{3}{4}\)

\(\Rightarrow \dfrac{2}{5}-x-1=\dfrac{3}{4}\)

\(\Rightarrow \left({\dfrac{2}{5}-1}\right)-x=\dfrac{3}{4}\)

\(\Rightarrow \dfrac{2-5}{5}-x=\dfrac{3}{4}\)

\(\Rightarrow x=\dfrac{-3}{5}-\dfrac{3}{4}\)

\(\Rightarrow x=\dfrac{-3.4-3.5}{20}\)

\(\Rightarrow x=\dfrac{-27}{20}\) (loại).

b) \(| x – \dfrac{1}{3} | = \dfrac{2}{3}\)

c) \(4 | x – \dfrac{1}{2} | = \dfrac{1}{3}\)