Question

BT1: Tìm x, biết:

5) \(\text{|}x+\dfrac{1}{3}\text{|}+\text{|}x+\dfrac{1}{5}\text{|}+\text{|}x+\dfrac{1}{15}\text{|}=4x\)

Answer 1

\(\left|x+\dfrac{1}{3}\right|+\left|x+\dfrac{1}{5}\right|+\left|x+\dfrac{1}{15}\right|=4x\)

Mà \(\left\{{}\begin{matrix}\left|x+\dfrac{1}{3}\right|\ge0\\\left|x+\dfrac{1}{5}\right|\ge0\\\left|x+\dfrac{1}{15}\right|\ge0\end{matrix}\right.\)

\(\Leftrightarrow\left|x+\dfrac{1}{3}\right|+\left|x+\dfrac{1}{5}\right|+\left|x+\dfrac{1}{15}\right|\ge0\)

\(\Leftrightarrow4x\ge0\)

\(\Leftrightarrow x+\dfrac{1}{3}+x+\dfrac{1}{5}+x+\dfrac{1}{15}=4x\)

\(\Leftrightarrow3x+1=4x\)

\(\Leftrightarrow x=1\)

Vậy ..