（1）3x/8y×16y²/27x² =(3/8×16/27)×(y/x)=2y/9x（2）（2xy-x²）÷x-2y/xy =x(2y-x)×[xy/(x-2y)]=-x²y(3)2x-6/x²-4x+4×2x-4/x-3=2(x-3)/(x-2)²×2(x-2)/(x-3)=4/(x-2)