Xy+(x+y)=19
xy(x+y)=84
xy=a U x+y=b
a+b=19 U a*b=84
по теореме Виета
1)a=12 U b=7
xy=12 Ux+y=4
x=3 y=4 или x=4 y=3
2)xy=4 U x+y=12
x=12-y
12y-y²=4
y²-12y+4=0
D=144-16=128 √D=8√2
y1=(12-8√2)/2=6-4√2⇒x1=12-6+4√2=6+4√2
y2=6+4√2⇒x2=12-6-4√2=6-4√2
Ответ ((3;4) (4;3) (6+4√2;6-4√2) (6-4√2;6+4√2)