已知a-b=8,ab=12,
(a-b)^2=8^2
a^2-2ab+b^2=64
a^2-2ab+b^2+4ab=64+4ab
(a+b)^2=112
a+b=±4√ 7
已知a-b=2,ab=12,
(a-b)^2=2^2
a^2-2ab+b^2=4
a^2-2ab+b^2+4ab=4+4ab
(a+b)^2=52
a+b=±2√13
1/2a^2b-ab+1/2ab^2
=1/2ab(a-2+b)
=1/2ab(a+b-2)
=1/2*12*(±2√13-2)
=±12√13- 12