3.|2x +1|= -12-(-21)
3. |2x+1| =9
|2x+1| =9: 3
|2x +1| = 3
\(\Rightarrow\)\(\orbr{\begin{cases}2x+1=3\\2x+1=-3\end{cases}}\)\(\Rightarrow\orbr{\begin{cases}2x=3-1\\2x=-3-1\end{cases}}\)
\(\Rightarrow\orbr{\begin{cases}2x=2\\2x=-4\end{cases}}\Rightarrow\orbr{\begin{cases}x=2:2\\x=-4:2\end{cases}}\)
\(\Rightarrow\orbr{\begin{cases}x=1\\x=-2\end{cases}}\)
\(-12-3.\left|2x+1\right|=-21\)\(1\)
\(3.\left|2x+1\right|=-12-\left(-21\right)\)
\(3.\left|2x+1\right|=-12+21\)
\(3.\left|2x+1\right|=9\)
\(\left|2x+1\right|=9:3\)
\(\left|2x+1\right|=3\)
Trường hợp 1
\(2x+1=3\)
\(2x=2\)
\(x=1\)
Trường hợp 2
\(2x+1=-3\)
\(2x=-4\)
\(x=-2\)
VẬY x\(\in\){1 ; -2}
