应该是x/y=3吧：∴x=3y,代入原式,原式=【(3y)²-3y*y+y²】/【(3y)²+2*3y*y-3y²】=(7y²)/(12x²)=7/12（2）∵x+1/x=3∴x²+1/X²+2=9,x²+1/X²=7,（x²）²+x&...