Решить систему за 7 класс а)3х-5у=8 х=-у б)3(х-у)+5х=2(3х-2) 4х-2(х+у)=4-3у

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1

X=1; y=2

3х-5у=8
х=-у

-3у - 5у = 8
x = -y

-8y = 8
x = -y

x = 1
y = -1

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3(х-у)+5х=2(3х-2)
4х-2(х+у)=4-3у

3x - 3y + 5x = 6x - 4
4x - 2x - 2y = 4 - 3y

8x - 3y - 6x = -4
2x - 2y + 3y = 4

2x - 3y = -4
2x + y = 4

-4y = -8
2x + y = 4

y = 2
2x + 2 = 4

y = 2
2x = 2

x = 1
y = 2

а) 3x - 5y = 8, x = -y.
3(-y) - 5y = 8 => -3y - 5y = 8 => -8y = 8 => y = -1.
x = -(-1) = 1.
Ответ: (1; -1)
б) 3(x-y)+5x=2(3x-2), 4x-2(x+y)=4-3y.
3x-3y+5x = 6x-4 => 8x-3y = 6x-4 => 2x - 3y = -4
4x-2x-2y = 4-3y => 2x-2y = 4-3y => 2x + y = 4
(2x + y) - (2x - 3y) = 4 - (-4) => 4y = 8 => y = 2.
2x + 2 = 4 => 2x = 2 => x = 1.
Ответ: (1; 2)