简单的运算
(2e^x+e^x+2-1)/(e^x+1)=[(2e^x+2)+(e^x-1)]/(e^x+1)=[2(e^x+1)+(e^x-1)]/(e^x+1)=2(e^x+1)/(e^x+1)+(e^x-1)/(e^x+1)=2+(e^x-1)/(e^x+1)
