1.x²-1/x²+4x+4÷(x+1)×x²-4/x-1
=x²-1/(x+2)²×1/x+1 ×(注：乘号) x²-4/x-1
=(x²-1)(x+2)(x-2)/(x+2)²(x²-1)
=x-2/x+2
2.x²-4/ x²+4x+4
=(x+2)(x-2)/(x+2)²
=x-2/x+2
3.2x-6/x+3÷9-3x/x²-9
=2(x-3)/x+3 × (x+3)(x-3)/-3(x-3)
=-2(x-3)/3
=-2/3 x+2(注：负3分之2 x加2
4.=27 a的九次方/(x+y)的立方 × (x+y)(x-y)
=27a的九次方/(x-y)的平方