a) \(3x^2-3xy-2x+2y\)
\(=3x\left(x-y\right)-2\left(x-y\right)\)
\(=\left(3x-2\right)\left(x-y\right)\)
b) \(6x^2+3xy-2ax-ay\)
\(=3x\left(2x+y\right)-a\left(2x+y\right)\)
\(=\left(3x-a\right)\left(2x+y\right)\)
c) \(x^3-6x^2+9x\)
\(=x\left(x^2-6x+9\right)\)
\(=x\left(x-3\right)^2\)
d) \(2xy-x^2-y^2+25\)
\(=25-\left(x-y\right)^2\)
\(=\left(5-x+y\right)\left(5+x-y\right)\)
f) \(2a^2-4ab+2b^2-8c^2\)
\(=2\left[\left(a-b\right)^2-4c^2\right]\)
\(=2\left(a-b-c\right)\left(a-b+c\right)\)