Verified answer

1.

[tex]\displaystyle\bf\\\left \{ {{x -3 y = 7} \atop {2x - 3y = - 3 }} \right. \\ \displaystyle\bf\\\left \{ {{x = 7 + 3y} \atop {2(7 + 3y) - 3y = - 3 }} \right. \\ \\ 14 + 6y - 3y = - 3 \\ 3y = - 3 - 14 \\ \\ 3y = - 17 \\ y = - \frac{17}{3} \\ y = - 5 \frac{2}{3} \\ \\ x - 3 \times ( - \frac{17}{3} ) = 7 \\ x + 17 = 7 \\ x = 7 - 17 \\ x = - 10[/tex]

Ответ: ( - 10 ; - 5 2/3 )

2.

[tex]\displaystyle\bf\\\left \{ {{3x + 5y = 19 \: \: | \times 2} \atop {7x - 10y = 1 }} \right. \\ \displaystyle\bf\\ + \left \{ {{6x + 10y = 38} \atop {7x - 10y = 1 }} \right. \\ \\ 6x + 7x = 38 + 1 \\ 13x = 39 \\ x = 39 \div 13 \\ x = 3 \\ \\ 3 \times 3 + 5y = 19 \\ 9 + 5y = 19 \\ 5y = 19 - 9 \\ 5y = 10 \\ y = 10 \div 5 \\ y = 2[/tex]

Ответ: ( 3 ; 2 )

3.

х грн - стоит 1 аккумулятор

у грн - стоит 1 батарейка

[tex]\displaystyle\bf\\\left \{ {{2x + 3y = 97.5} \atop {x = 18y }} \right. \\ \\ 2 \times 18y + 3y = 97.5 \\ 36y + 3y = 97.5 \\ 39y = 97.5 \\ y = 97.5 \div 39 \\ y = 2.5 \\ \\ x = 1.8 \times 25 \\ x = 45[/tex]

Ответ: 1 аккумулятор стоит 45 грн, 1 батарейка стоит 2,5 грн