Решите систему уравнений: x^2 - 4y^2 = 0; 2x + 5y = 18. с пояснением, .

2x + 5y = 18
X = 9 - 2,5y
X^2 = 81 - 45y + 6,25y^2
81 - 45y + 6,25y^2 - 4y^2 = 0
2,25y^2 - 45y + 81 = 0
2,25( y^2 - 20y + 36 ) =
D = 400 - 144 = 256 = 16^2
y1 = ( 20 + 16 ) : 2 = 18
y2 = ( 20 - 16 ) : 2 = 2
X = 9 - 2,5y
X1 = 9 - 2,5•18 = 9 - 45 = - 36
X2 = 9 - 2,5•2 = 4
ответ ( - 36 ; 18 ) ; ( 4 ; 2 )