（x-3/x^2+3x+2）*（x^2/x^2-4x+3）
=(x-3)/(x+2)(x+1)×x²/(x-3)(x-1)
=x²/(x+2)(x+1)(x-1)
怀疑本题是
（x-3/x^2+3x+2）*（x^2 -1 /x^2-4x+3）,
=(x-3)/(x+2)(x+1)×(x+1)(x-1)/(x-3)(x-1)
=1/(x+2)
（x^2-1/x-1÷x^2-x/x^2-2x+1）
=(x+1)(x-1)/(x-1)×(x-1)²/x(x-1)
=(x+1)×(x-1)/x
=(x²-1)/x