Решите систему уравнений xy=7 x+y=8

Y = 8-x

x(8-x) = 7
-x^2 + 8x - 7 =0

x^2 - 8x + 7 = 0
x = 1
x = 7 
по теореме виета

y=7
y = 1

ответ (1;7) (7:1)

Х = 8 - y
( 8 - y )•y = 7
8y - y^2 = 7
y^2 - 8y + 7 = 0
D = 64 - 28 = 36 = 6^2
y1 = ( 8 + 6 ) : 2 = 7
y2 = ( 8 - 6 ) : 2 = 1
X1 = 8 - 7 = 1
X2 = 8 - 1 = 7
ответ ( 1 ; 7 ) ; ( 7 ; 1 )