Lionel Messi
19/03/2017 at 11:43
FA KAKALOTS 06/02/2018 at 12:30
(x + y)2 = 9
<=> x2 + 2xy + y2 = 9 (1)
(x  y)2 = 1
<=> x2  2xy + y2 = 1 (2)
(1)  (2) => 4xy = 8 => xy = 2
=> x2 + 2xy + y2 = 9
<=> x2 + 4 + y2 = 9
<=> x2 + y2 = 5

Hồ Thu Giang 19/03/2017 at 14:36
(x + y)^{2} = 9
<=> x^{2} + 2xy + y^{2} = 9 (1)
(x  y)^{2} = 1
<=> x^{2}  2xy + y^{2} = 1 (2)
(1)  (2) => 4xy = 8 => xy = 2
=> x^{2} + 2xy + y^{2} = 9
<=> x^{2} + 4 + y^{2} = 9
<=> x^{2} + y^{2} = 5