\(3\left(x-1\right)\left(x-2\right)-x\left(3x+1\right)\left(1-x\right)\)
\(=3\left(x-1\right)\left(x-2\right)+x\left(x-1\right)\left(3x+1\right)\)
\(=\left(x-1\right)\left[3\left(x-2\right)+x\left(3x+1\right)\right]\)
\(=\left(x-1\right)\left(3x-6+3x^2+x\right)\)
\(=\left(x-1\right)\left(3x^2+4x-6\right)\)
#Ayumu