\(a,5x^2-x=x\left(5x-1\right)\)
\(b,z^3-z^2+z=z\left(z^2-z+1\right)\)
\(c,a\left(a-2\right)+a-2=\left(a-2\right)\left(a+1\right)\)
\(d,12m\left(2-n\right)-18n\left(n-2\right)\)
\(=12m\left(2-n\right)+18n\left(2-n\right)\)
\(=6\left(2-n\right)\left(2m+3n\right)\)
\(e,\left(x^2-4x\right)+\left(12x-48\right)\)
\(=x\left(x-4\right)+12\left(x-4\right)\)
\(=\left(x-4\right)\left(x+12\right)\)