[ ( x-4 ) / ( x^2 - 1 ) ] ÷ [ ( x^2 - 3x - 4 ) / ( x^2 + 2x + 1 ) ] + （1 / x-1 ）
=（x-4)/[(x+1)(x-1)×(x+1)²/[(x-4)(x+1)]+1/(x-1)
=1/(x-1)+1/(x-1)
=2/(x-1)
2/2√2
=√2/2