解:1:1/2ab³=5ac/10a²b³c; 2/5a²b²c=4b/10a²b³c; 2:a/2xy=3ax/6x²y; b/3x²=2y/6x²y; 3: 3c/2ab²=12c³/8ab²c²; -a/8bc²=-a²c/8ab²c²; 4:1/(y-1)=(y+1)/(y²-1) 1/(y+1)=(y-1)/(y²-1)