3x-4/(x-1)(x-2)=A/(x-1)+B/(x-2)(3x-4)/(x-1)(x-2)=[A(x-2)+B(x-1)]/(x-1)(x-2)(3x-4)/(x-1)(x-2)=[(A+B)x-(2A+B)]/(x-1)(x-2)两边恒等A+B=32A+B=4A=1B=2
A/(x-1)+B/(x-2)=[(A+B)x-(2A+B)]/(x-1)(x-2) 所以A+B=3,2A+B=4 A=1,B=2 A=1 B=2时,x也不能取1,2,否则分母就等于0,没意义了