Системы уравнений 1) x^2+y^2=13 xy=6 2) x-31y=4 x-5y=10

1) x=6/y
36/y^2+y^2=13
y^4-13y^2+36=0
D=25
(y1,2)^2=(13+-5)/2=9; 4
y1=3 y2=-3 y3=2 y4=-2
x1=2 x2=-2 x3=3 x4=-3
2)x=10+5y
10+5y-31y=4
10-26y=4
-26y=-14
y=14/26=7/13
x=10+35/13=12 9/13