Ответ: 1. (5;-4) (-4;5) 2. (-2;1)

1. x+y=1

xy=-20

x=1-y

(1-y)y=-20

-y²+y=-20

-y²+y+20=o

y1=5 y2=-4

x1=1-5=-4

x2=1-(-4)=5

2. x+3y=1

x²+2xy-y²=-1

x=1-3y

(1-3y)²+2y(1-3y)-y²=-1

1-6y+9y²+2y-6y²-y²=-1

2-4y+2y²=0

y²-2y+1=0

(y-1)²=0

y-1=0

y=1

x=1-3*1=-2