Question

помогите срочно 1 вариант​

Answer 1

1.

$\displaystyle\bf\\\left \{ {{3x + y = 7} \atop {9x - 4y = - 7 }} \right. \\ \displaystyle\bf\\\left \{ {{y = 7 - 3x} \atop {9x - 4(7 - 3x) = - 7 }} \right. \\ \\ 9x - 28 + 12x = - 7 \\ 21x = - 7 + 28 \\ 21x = 21 \\ x = 21 \div 21 \\ x = 1 \\ \\ y = 7 - 3 \times 1 \\ = 7 - 3 \\ y = 4$

Ответ: ( 1 ; 4 )

2.

$\displaystyle\bf\\\left \{ {{x - y = 9 \: \: | \times 2} \atop {3x + 2y = 13 }} \right. \\ \displaystyle\bf\\ + \left \{ {{2x - 2y = 18} \atop {3x + 2y = 13 }} \right. \\ \\ 2x + 3x = 18 + 13 \\ 5x = 31 \\ x = 31 \div 5 \\ x = 6.2 \\ \\ 6.2 - y = 9 \\ y = 6.2 - 9 \\ y = - 2.8$

Ответ: ( 6,2 ; - 2,8 )

3.

$\displaystyle\bf\\\left \{ {{ \frac{2x + 1}{5} = \frac{y - 1}{2} } \atop {4x + 5y = 23 }} \right. \\ \displaystyle\bf\\\left \{ {{5(y - 1) - 2(2x + 1) = 0} \atop {4x + 5y = 23 }} \right. \\ \displaystyle\bf\\\left \{ {{5y - 5 - 4x - 2 = 0} \atop {4x + 5y = 23 }} \right. \\ \displaystyle\bf\\ + \left \{ {{ - 4x + 5y = 7} \atop {4x + 5y = 23 }} \right. \\ \\ 5y + 5y = 7+ 23 \\ 10y = 30 \\ y = 30 \div 10 \\ y = 3 \\ \\ 4x + 5 \times 3 = 23 \\ 4x + 15 = 23 \\ 4x = 23 - 15 \\ 4x = 8 \\ x = 8 \div 4 \\ x = 2$

Ответ: ( 2 ; 3 )