Question

Розв'яжіть систему рівнянь способом додавання: (4(x + 2) = 1 - 5у, (3(y+ 2) = 3 - 3x. У відповідь записати суму x + у.​

Answer 1

$\displaystyle\bf\\\left \{ {{4(x + 2) = 1 - 5y} \atop {3(y + 2) = 3 - 3x }} \right. \\ \displaystyle\bf\\\left \{ {{4x + 8 = 1 - 5y} \atop {3y + 6 = 3 - 3x }} \right. \\ \displaystyle\bf\\\left \{ {{4x + 5y = 1 - 8} \atop {3x +3y = 3 - 6 }} \right. \\ \displaystyle\bf\\\left \{ {{4x + 5y = - 7 \: \: | \times ( - 3)} \atop {3x + 3y = - 3 \: \: | \times 5}} \right. \\ \displaystyle\bf\\ + \left \{ {{ - 12x - 15y = 21} \atop {15x + 15y = - 15 }} \right. \\ \\ 15x - 12x = 21 - 15 \\ 3x = 6 \\ x = 6 \div 3 \\ x = 2 \\ \\ 4 \times 2 + 5y = - 7 \\ 8 + 5y = - 7 \\ 5y = - 7 - 8 \\ 5y = - 15 \\ y = - 15 \div 5 \\ y = - 3 \\ \\ x + y = 2 - 3 = - 1$

Ответ: - 1