来自李永昌的问题
(a+b+c)(a+b-c)=[()+()][()-()](a-b+c)(a+b-c)=[()+()][()-()](a+b+c)(a-b-c)=[()+()][()-()]
(a+b+c)(a+b-c)=[()+()][()-()]
(a-b+c)(a+b-c)=[()+()][()-()]
(a+b+c)(a-b-c)=[()+()][()-()]


(a+b+c)(a+b-c)=[()+()][()-()](a-b+c)(a+b-c)=[()+()][()-()](a+b+c)(a-b-c)=[()+()][()-()]
(a+b+c)(a+b-c)=[()+()][()-()]
(a-b+c)(a+b-c)=[()+()][()-()]
(a+b+c)(a-b-c)=[()+()][()-()]
1.[(a+b)+(C)][(a+b)-(c)]
2.[a+(b-c)][a-(b-c)]
3.[a+(b+c)][a-(b+c)]