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Не виконуючи побудови знайти координати точок:

7x+4y=9 i 2x+5y=--9

Answer 1

$\displaystyle\bf\\\left \{ {{7x + 4y = 9 \: \: | \times ( - 2)} \atop {2x + 5y = - 9 \: \: | \times 7 }} \right. \\ \displaystyle\bf\\ + \left \{ {{ - 14x - 8y = - 18} \atop {14x + 35y = - 63 }} \right. \\ \\ 35y - 8y = - 35 - 18 \\ 27y = - 81 \\ y = - 81 \div 27 \\ y = - 3 \\ \\ 2x + 5 \times ( - 3) = - 9 \\ 2x - 15 = - 9 \\ 2x = - 9 + 15 \\ 2x = 6 \\ x = 6 \div 2 \\ x = 3$

Ответ: ( 3 ; - 3 )