To simplify the expression (2mn-3n^2)-((5mn-2m^2)-(4mn-3n^2)),

First, distribute the negative sign inside the parentheses:

= (2mn - 3n^2) - (5mn - 2m^2) + (4mn - 3n^2)

Now, distribute the negative sign in front of the second set of parentheses:

= 2mn - 3n^2 - 5mn + 2m^2 + 4mn - 3n^2

Combine like terms:

= (2mn - 5mn + 4mn) + (-3n^2 + 2m^2 - 3n^2)

= 1mn + (- 3n^2 + 2m^2 - 3n^2)

= 1mn - 6n^2 + 2m^2

Therefore, (2mn-3n^2)-((5mn-2m^2)-(4mn-3n^2)) simplifies to 1mn - 6n^2 + 2m^2.