Система х^2+3ху-у^2+2х-5у=-64
х-у=-7

х^2+3ху-у^2+2х-5у=-64

х-у=-7

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x=y - 7

(y-7)^2 + 3y(y-7) - y^2 + 2(y-7) - 5y = -64

y^2 - 14y + 49 + 3y^2 - 21y - y^2 + 2y - 14 - 5y + 64 =0

3y^2 - 38y + 99 = 0

D = 38*38 - 4*3*99 = 256 = 16^2

y12= (38 +- 16)/6 = 9   11/3

y1 = 9   x1=y-7=2

y2 = 11/3   x2=11/3 - 7 = -10/3

ответ (-10/3  11/3)( 2  9)