Ответы и объяснения

2012-12-28T06:55:23+00:00

\left \{ {{x-y=7} \atop {xy=-12}} \right.
\left \{ {{x=7-y} \atop {xy=-12}} \right.

y(7-y)=-12
7y-y²=-12

y²-7y-12=0

D=49-4·12=1

y₁=7+1/2=4

y₂=7-1/6=3

x₁=7-4=3

x₂=7-3=4

\left \{ {{x_1=3} \atop {y_1=4}} \right.  \left \{ {{x_2=4} \atop {y_2=3}} \right.