[2/(a-1)-1/(a+1)]÷[(a²-9)/(a²-1)]=(2a+2-a+1)/(a²-1)X[(a²-1)/(a²-9)]=(a+3)/(a+3)(a-3)=1/(a-3)=1/(√2+3-3)=1/(√2)=(√2)/2
