Solution: (1) The circumference of a square consists of four arcs, which is exactly the circumference of a circle with a diameter of AB and a circle with a diameter of BC. Because AB=y, BC=x, π x+π y = 628. Because π = 3. 14, it is 3. 14x+3.

(2)① The area of rectangle is xy, the area of circle AB is π×, and the area of circle BC is π×.

So w = 428 xy+400×π×+400×π× = 428 xy+400×π×+400×π× = 428 × (200-x)+400× 3.14×+400× 3.6543.100010000006

That is, w = 200-40000x+12560000;

(2) Only the government investment of 65.438 billion yuan cannot complete the construction task of this project, for the following reasons:

From ① we know that W = 200+ 1.056× >, so we can't;

③ From the meaning of the question, x≤y, that is, x≤ (200-x), then the solution is: x≤80, so 0≤x≤80.

According to the meaning of the question: W=200+ 1.056×=+6.842×, ranking =44 1, solved (please write down the reason), so you can only take x=79, so y = 200-79 = 1268.