(1)
a=2時(shí),
(1+2)/(1-2)=-3也屬于A,
(1-3)/(1+3)=-1/2也屬于A,
(1-1/2)/(1+1/2)=1/3也屬于A,
(1+1/3)/(1-1/3)=2也屬于,
∴A={2,-3,-1/2,1/3}
(2)
a=0時(shí),(1+0)/(1-0)=1
∵A里不含1
∴0不是A的元素.
設(shè)計(jì)a=5,
(1+5)/(1-5)=-3/2,
(1-3/2)/(1+3/2)=-1/5,
(1-1/5)/(1+1/5)=2/3,
(1+2/3)/(1-2/3)=5,
∴A={5,-3/2,-1/5,2/3}
(3)
根據(jù)(1)(2),能猜出
A中有且只有4個(gè)元素.
都是以下這4個(gè)類型的元素
a,
(1+a)/(1-a),
-1/a,
(a-1)/(a+1),