a, \(\left[{}\begin{matrix}2x+1=2021\\2x+1=-2021\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=1010\\x=-1011\end{matrix}\right.\)
b, \(\left[{}\begin{matrix}x^2-4x-1=31\\x^2-4x-1=-31\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x^2-4x-32=0\\x^2-4x+30=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=8;x=-4\\\left(x-2\right)^2+26=0\left(voli\right)\end{matrix}\right.\)
c, \(\left[{}\begin{matrix}x-1=3x-5\\x-1=5-3x\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}2x=4\\4x=6\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=2\\x=\dfrac{3}{2}\end{matrix}\right.\)
d, \(\left[{}\begin{matrix}x^2-x-6=0\\x^2+x-6=0\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x=3;x=-2\\x=2;x=-3\end{matrix}\right.\)
a: \(\Leftrightarrow\left[{}\begin{matrix}2x+1=2021\\2x+1=-2021\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=1009\\x=-1010\end{matrix}\right.\)
b: \(\Leftrightarrow\left[{}\begin{matrix}x^2-4x-1=31\\x^2-4x-1=-31\end{matrix}\right.\Leftrightarrow x^2-4x-32=0\)
=>(x-8)(x+4)=0
=>x=8 hoặc x=-4
