1)

[tex]\displaystyle\bf\\\left \{ {{y = x - 8} \atop {y = 5x + 8 }} \right. \\ \\ 5x + 8 = x - 8 \\ 5x - x = - 8 - 8 \\ 4x = - 16 \\ x = - 16 \div 4 \\ x = - 4 \\ \\ y = - 4 - 8 \\ y = - 12[/tex]

Ответ: ( - 4 ; - 12 )

2)

[tex]\displaystyle\bf\\\left \{ {{5y - 15x = 45} \atop { - 30x - 90 = 10y }} \right. \\ \displaystyle\bf\\ + \left \{ {{5y - 15x = 45} \atop { - 5y - 15x = 45 }} \right. \\ \\ - 15x - 15x = 45 + 45 \\ - 30x = 90 \\ x = 90 \div ( - 30) \\ x = - 3 \\ \\ 5y - 15 \times ( - 3) = 45 \\ 5y + 45 = 45 \\ 5y = 45 - 45 \\ 5y = 0 \\ y = 0[/tex]

Ответ: ( - 3 ; 0 )