X2-2y=54 y=x-3 первый x в квадрате

$x^{2} - 2y = 54 \\ y = x - 3$

${x}^{2} - 2(x - 3) = 54 \\ y = x - 3$

${x}^{2} - 2x + 6 = 54 \\ y = x - 3$

${x}^{2} - 2x - 48 = 0 \: \: (1)\\ y = x - 3$

$(1) \: \: \: {x}^{2} - 2x - 48 = 0 \\ d = {2}^{2} - 4 \times ( - 48) = 4 + 192 = 196 = {14}^{2} \\ x_{1} = \frac{2 + 14}{2} = \frac{16}{2} = 8 \\ x_{2} = \frac{2 - 14}{2} = - \frac{12}{2} = - 6$

$x_{1} = 8 \\ y_{1} = 8 - 3 = 5$

$x_{2} = - 6 \\ y_{2} = - 6 - 3 = - 9$
Ответ: (8;5) (-6;-9)