x + y = 5
2y^2 - 5x = 8
Решение
x = 5 - y
2y^2 - 5( 5 - y ) = 8
2y^2 - 25 + 5y - 8 = 0
2y^2 + 5y - 33 = 0
D = 25 + 264 = 289 = 17^2
y1 = ( - 5 + 17 ) : 4 = 3
y2 = ( - 5 - 17 ) : 4 = - 5,5
x1 = 5 - 3 = 2
x2 = 5 + 5,5 = 10,5
Ответ ( 2 ; 3 ) ; ( 10,5 ; - 5,5 )