3x^3y-6x^2y^2-9xy

The given expression is: 3x^3y - 6x^2y^2 - 9xy

This expression can be simplified by factoring out the common factor "3xy" from each term:

3xy(x^2 - 2xy - 3)

Therefore, the simplified expression is: 3xy(x^2 - 2xy - 3)