a: \(A=2x^2-2x^2-x-5+\left|7x-1\right|\)
=|7x-1|-x-5
Trường hợp 1: x>=1/7
A=7x-1-x-5=6x-6
Trường hợp 2: x<1/7
A=1-7x-x-5=-8x-4
b: Để A=2 thì |7x-1|-x-5=2
=>|7x-1|=x+7
\(\Leftrightarrow\left\{{}\begin{matrix}x>=-7\\\left(7x-1\right)^2-\left(x+7\right)^2=0\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}x>=-7\\\left(7x-1-x-7\right)\left(7x-1+x+7\right)=0\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}x>=-7\\\left(6x-8\right)\left(8x+6\right)=0\end{matrix}\right.\Leftrightarrow x\in\left\{\dfrac{4}{3};-\dfrac{3}{4}\right\}\)
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