Ответы и объяснения

2013-12-02T00:38:06+04:00
 \left \{ {{x+y+xy=11} \atop {xy(x+y)=30}} \right.
Пусть: x+y = a , xy = b
Тогда:
 \left \{ {{a+b=11} \atop {ab=30}} \right.
 \left \{ {{a=11-b} \atop {(11-b)b=30}} \right.
11b- b^{2} =30
 b^{2} -11b+30=0
(b-6)(b-5)=0
 b_{1} =6    b_{2} =5
 a_{1} =5    a_{2} =6

1)  \left \{ {{x+y=5} \atop {xy=6}} \right.
2)  \left \{ {{x+y=6} \atop {xy=5}} \right.

Ответ: (2;3). (1;5)