a)
\(3x\left(x+1\right)-2x\left(x+2\right)=-1-x\)
\(3x^2+3x-2x^2-4x+1+x=0\)
\(3x^2-2x^2+3x-4x+x+1=0\)
\(x^2+1=0\)
\(x^2=-1\left(voli\right)\)
b)
\(4x\left(x-2021\right)-x+2021=0\)
\(4x\left(x-2021\right)-\left(x-2021\right)=0\\ \left(x-2021\right)\left(4x-1\right)=0\\ \left[{}\begin{matrix}x-2021=0\\4x-1=0\end{matrix}\right.\left[{}\begin{matrix}x=2021\\x=\dfrac{1}{4}\end{matrix}\right.\)
c)
\(\left(x-4\right)^2-36=0\\ \left(x-4-6\right)\left(x-4+6\right)=0\\ \left(x-10\right)\left(x+2\right)=0\\ \left[{}\begin{matrix}x-10=0\\x+2=0\end{matrix}\right.\left[{}\begin{matrix}x=10\\x=-2\end{matrix}\right.\)
d)
\(x^2+8x+16=0\\ \left(x+4\right)^2=0\\ =>x+4=0\\ x=-4\)
