x-y=7
xy=-12
x=7+y
xy=-12
(7+y)y=-12
7y+y²=-12
y²+7y+12=0
y²+3y+4y+12=0
y(y+3)+4(y+3)=0
(y+4)(y+3)=0
y=-4 ∨ y=-3
x=7+(-4) ∨ x=7+(-3)
x=3 ∨ x=4
х = 7 + у
у(у+7) = -12
у²+7у+12 = 0
Д = 49-48=1
у1 = (-7-1)/2 = -4
у2 = (-7+1)/2 = -3
у = -4 или у = -3
х = 3 х = 4
ответ. (3, -4); (4, -3).
