[(1-x)/(x+1)-1]÷2x／(x²-1)=[(1-x-x-1)/(x+1)]÷2x／(x²-1)=-2x/(x+1)÷2x／(x²-1)=-2x/(x+1)*(x²-1)/2x=-(x²-1)/(x+1)=-(x-1)(x+1)/(x+1)=-(x-1)=1-x=1-(1-√2 )=1-1+√2 =√2