绝对值项恒非负,两绝对值项之和=0,两绝对值项分别=0x-2=0 x=2y-4=0 y=4y=x+21/(xy)+1/[(x+2)(y+2)]+1/[(x+4)(y+4)]+...+1/[(x+1994)(y+1994)]=1/[x(x+2)]+1/[(x+2)(x+4)]+1/[(x+4)(x+6)]+...+1/[(x+1994)(x+1996)]=(...