(1)x=999,y=998,(2)x=-999,y=-998 (3)x=999,y=-998,(4)x=-999,y=998 1997是素数,故1997仅有分解式1997=1997*1 由x^2-y^2=1997得 (x+y)(x-y)=1997*1 故有4种情况:(1)x+y=1997 x-y=1 得x=999 y=998 (2)x+y=-1997 x-y=-...