{1+ [(x+1)(x-2)]分之(2x-4)}/ (x的平方-1)分之(x+3)
=[(x+1)(x-2)]分之（x²-x-2+2x-4）× (x+3)分之(x²-1)
=(x-2)分之(x²+x-6) × (x+3)分之(x-1)
=(x-2)分之(x+3)(x-2) × (x+3)分之(x-1)
=x-1
已知x=6,那么原式=x-1=6-1=5