As shown in the figure, in Rt△ABC, the hypotenuse AB = 5cm, BC = a cm, AC = b cm, A > B, A and B are two equations.

(1) Find the values of a and b; ?

(2) If △A'B'C and △ABC are completely coincident at the beginning, then △ABC is fixed, and △A'B'C moves to the left along the line where BC is located at the speed of 1cm/s ...?

I) let △A'B'C and △ABC? The area of the overlapping part is y square centimeter, find the functional relationship between y and x, and write the value range of x; ?

Ii) After a few seconds, the area of the overlapping part is equal to 3/8 cm2? (9 points)