\(4x\left(3x^2-x\right)-\left(2x+3\right)\left(6x^2-3x+1\right)\\ =12x^3-4x^2-12x^3+6x^2-2x-18x^2+9x-3\\ =-16x^2+7x-3\)

câu 1 thiếu 1 th nx .-. 

\(\sqrt{9x^2}=2x+1\\ \Leftrightarrow\sqrt{\left(3x\right)^2}=2x+1\\ \Leftrightarrow\left|3x\right|=2x+1\)

th1 :\(3x\ge0\Leftrightarrow x\ge0\Rightarrow\left|3x\right|=3x\)

\(\Rightarrow3x=2x+1\\ \Leftrightarrow3x-2x=1\\ \Leftrightarrow x=1\)

th2 : \(3x< 0\Leftrightarrow x< 0\Rightarrow\left|3x\right|=-3x\)

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

~~~~~~~~~~~~~~~~~~~~~~~~~~~~

\(\sqrt{x^2}=7\\ \Leftrightarrow\left|x\right|=7\\ \Leftrightarrow\left[{}\begin{matrix}x=7\\x=-7\end{matrix}\right.\)

\(1)\\ a,31-x=11+9\\ 31-x=20\\ x=11\\ b,x-3=\left(-6\right)+\left(-9\right)\\ x-3=-15\\ x=-12\\ 2)\\ a,\left|x\right|=5\\ \Leftrightarrow\left[{}\begin{matrix}x=5\\x=-5\end{matrix}\right.\\ b,\left|x\right|+13=0\\ \Rightarrow\left|x\right|=-13\\ \Rightarrow x=-13\\ c,\left|x-11\right|=12\\ \Leftrightarrow\left[{}\begin{matrix}x-11=12\\x-11=-12\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=23\\x=-1\end{matrix}\right.\\ d,\left|x+16\right|=3\\ \Leftrightarrow\left[{}\begin{matrix}x+16=3\\x+16=-3\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=-13\\x=-19\end{matrix}\right.\)

:> gheeeeeeeeeee

:\ cj xoá ddiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii, nha

ai ngăn cản toy k xóa câu trl nì đi:^ 

\(\rightarrow\) Xoá đi cj .-. 

.-. ... hết bị khoá r ak ? 

\(\dfrac{50}{3+x}=\dfrac{23}{2-1}\\ \Leftrightarrow23\left(3+x\right)=50\left(2-1\right)\\ \Leftrightarrow23\left(3+x\right)=50\\ \Leftrightarrow3+x=\dfrac{50}{23}\\ \Leftrightarrow x=-\dfrac{19}{23}\)