\(M=x^4-2x^3+3x^2-x+2\)
\(M=x^4-x^3+x^2+2x^2-2x+2\)
\(M=x^2\left(x^2-x\right)-x\left(x^2-x\right)+2\left(x^2-x\right)+2\)
\(M=\left(x^2-x\right)\left(x^2-x+2\right)+2\)
\(M=4.\left(4+2\right)+2\)( Vì \(x^2-x=4\))
\(M=24+2=26\)
Vậy M = 26 khi \(x^2-x=4\)