a) \(\left|7x-4\right|=-7\)
Mà \(\left|7x-4\right|\ge0\forall x\)
\(\Rightarrow\) phương trình vô nghiệm
b) \(\left|3x-4\right|=\left|7x+5\right|\)
\(\Rightarrow\left[{}\begin{matrix}3x-4=7x+5\\3x-4=-7x-5\end{matrix}\right.\)
\(\Rightarrow\left[{}\begin{matrix}x=-\dfrac{9}{4}\\x=-\dfrac{1}{10}\end{matrix}\right.\)
Vậy ...
a: \(\left|7x-4\right|=-7\)
mà |7x-4| luôn không âm
nên \(x\in\varnothing\)
b: |3x-4|=|7x+5|
=>7x+5=3x-4 hoặc 7x+5=4-3x
=>4x=-9 hoặc 10x=-1
=>x=-9/4 hoặc x=-1/10
c: |x-4|=-4x+2
\(\Leftrightarrow\left\{{}\begin{matrix}\left(x-4\right)^2=\left(-4x+2\right)^2\\-4x+2>=0\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}\left(4x-2-x+4\right)\left(4x-2+x-4\right)=0\\-4x>=-2\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}x< =\dfrac{1}{2}\\\left(3x+2\right)\left(5x-6\right)=0\end{matrix}\right.\Leftrightarrow x=-\dfrac{2}{3}\)
b) \(TH1=>3x-4=7x+5 =>x=9/4\)
\(TH2 .3x-4=-7x-5 x=-0,1\)
a) loại vì |a|≥0