(a的平方-4a+4)分之（a+1)(a-2) - (a的平方-2a)分之a÷（a-2)分之a
=(a-2)²分之（a+1)(a-2) - [a(a-2)]分之a × [a分之(a-2)]
=(a-2)分之(a+1) - a分之1
=[a(a-2)]分之[a(a+1)-(a-2)]
=[a(a-2)]分之(a²+2)