1) х+(у-(х-у))= 2) (4а^2-5в^2)(5а^2-4в^2)= 3) (а^2+3ав-2в^2(2а^2-3в)=

Let's simplify each expression step by step.

1. Expression: \( x + (y - (x - y)) \)

   Simplifying the inside brackets first: \[ y - (x - y) = y - x + y = 2y - x \] Now substitute this back into the expression: \[ x + (2y - x) = x + 2y - x = 2y \]

   Final Answer: \( 2y \)

2. Expression: \( (4a^2 - 5b^2)(5a^2 - 4b^2) \)

   Apply the distributive property (FOIL method): \[ = 4a^2 \cdot 5a^2 + 4a^2 \cdot (-4b^2) - 5b^2 \cdot 5a^2 - 5b^2 \cdot (-4b^2) \] Simplifying each term: \[ = 20a^4 - 16a^2b^2 - 25b^2a^2 + 20b^4 \] Combine like terms: \[ = 20a^4 - (16 + 25)a^2b^2 + 20b^4 = 20a^4 - 41a^2b^2 + 20b^4 \]

   Final Answer: \( 20a^4 - 41a^2b^2 + 20b^4 \)

3. Expression: \( a^2 + 3ab - 2b^2(2a^2 - 3b) \)

   Start with the multiplication: \[ -2b^2(2a^2 - 3b) = -4a^2b^2 + 6b^3 \] Now, combine this with \( a^2 + 3ab \): \[ = a^2 + 3ab - 4a^2b^2 + 6b^3 \]

   There are no like terms to combine further, so:

   Final Answer: \( a^2 + 3ab - 4a^2b^2 + 6b^3 \)

To summarize the answers:

1. \( 2y \)
2. \( 20a^4 - 41a^2b^2 + 20b^4 \)
3. \( a^2 + 3ab - 4a^2b^2 + 6b^3 \)