即(3x-4y)(x+y)=03x=4y或x=-y若3x=4yy=3x/4则y²=9x²/16,xy=3x²/4原式=(3x²/4-3x²)/(9x²/8-15x²/4-3x²)=-11881/352若y=-x则y²=x²,xy=-x²原式=(-x²-3x&s...