(2) Prove that if A belongs to A,1(1-a) belongs to A,

Let b =1/(1-a); 1/b = 1-a； a = 1- 1/b； 1-a = 1-( 1- 1/b)= 1/b；

Because1-a =1/b; So1/(1-a) = b; And because b= 1/( 1-a) belongs to a.

So if a belongs to a; Then 1- 1/a belongs to a.

Certificate of completion