Question

Tìm x, biết: |3x + 6| + |4x - 3| = 0

Answer 1

Do \(\left|3x+6\right|,\left|4x-3\right|\ge0\)

\(\Rightarrow\left\{{}\begin{matrix}3x+6=0\\4x-3=0\end{matrix}\right.\)

\(\Rightarrow\left\{{}\begin{matrix}x=-2\\x=\dfrac{3}{4}\end{matrix}\right.\)( vô lý)

Vậy \(S=\varnothing\)

Answer 2

\(|3x+6|+|4x-3|=0\)

<=> \(\left[{}\begin{matrix}3x+6+4x-3=0\\-3x-6-4x+3=0\\3x+6-4x+3=0\\-3x-6+4x-3=0\end{matrix}\right.\)

<=> \(\left[{}\begin{matrix}7x=-3\\-7x=3\\-x=-9\\x=9\end{matrix}\right.\)

<=> \(\left[{}\begin{matrix}x=\dfrac{-3}{7}\\x=9\end{matrix}\right.\)