(5x²-3y²)-[(5x²-2xy-y²)-(x²-2xy-y²)｝,其中x=2,y=-二分之一.先化简,后求值.

(5x²-3y²)-[(5x²-2xy-y²)-(x²-2xy-y²)｝,其中x=2,y=-二分之一.先化简,后求值.
(5x²-3y²)-[(5x²-2xy-y²)-(x²-2xy-y²)｝,其中x=2,y=-二分之一.先化简,后求值.

(5x²-3y²)-[(5x²-2xy-y²)-(x²-2xy-y²)｝,其中x=2,y=-二分之一.先化简,后求值.
(5x²-3y²)-[(5x²-2xy-y²)-(x²-2xy-y²)]
＝5x²-3y²-[5x²-2xy-y²-x²+2xy+y²]
＝5x²-3y²-[4x²]
＝5x²-3y²-4x²
＝x²-3y²
＝2²-3（1/2）²
＝4-3/4
＝13/4