Ответ:
x = 5
y = 7
Пошаговое объяснение:
{x - 2y = -9
{7x - 4y = 7
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{x = 2y - 9
{7x - 4y = 7
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7 * (2y - 9) - 4y = 7
14y - 63 - 4y = 7
10y = 70
y = 7
x = 2 * 7 - 9
x = 14 - 9
x = 5