f(2)=f(2-3)=f(-1)=-f(1)>-1即2a-1>-1a>0
f(x)=f(-x)=>f(2)=f(-2)=2a-1且f(x)=f(-x)=>f(1)=f(3-2)=f(-2)=f(2)=2a-1<1 => a<1