Với \(x+y+z+t=0\Leftrightarrow x+y+z=-t\)
\(\Leftrightarrow M=\dfrac{-t}{t}=-1\\ \Leftrightarrow\left(M-1\right)^{2020}=0\)
Với \(x+y+z+t\ne0\)
\(\Leftrightarrow M=\dfrac{3\left(x+y+z+t\right)}{x+y+z+t}=3\left(\text{tc dtsbn}\right)\\ \Leftrightarrow\left(M-1\right)^{2020}=\left(3-1\right)^{2020}=2^{2020}\)