Lgx+lgy=lg10 x^2+y^2=16

Question

Lgx+lgy=lg10
x^2+y^2=16

Answer 1

Lg(x+y)=Lg10, x+y=10, x = 10 - y
(10-y)^2 + y^2=16
100 - 20y +y^2 +y^2 = 16
2y^2 - 20y + 84 = 0
D = 8^2
y1 = 7
y2 = 3
x1 = 10 - 7 = 3
x2= 10 - 3 = 7
То есть  x = 3, y = 7 или x = 7, y = 3
Не имеет значения.