Решите систему уравнений

Решите задачу:

$\left \{ {{5^{x-1}*7^y=7^{-1}} \atop {y=x-2}} \right. \\ \left \{ {{5^{x-1}*7^{x-2}=7^{-1}} \atop {y=x-2}} \right. \\ \left \{ {{5^{x-1}*7^{x-1}*7^{-1}=7^{-1}} \atop {y=x-2}} \right. \\ \left \{ {{5^{x-1}*7^{x-1}=1} \atop {y=x-2}} \right. \\ \left \{ {{(5*7)^{x-1}=1} \atop {y=x-2}} \right. \\ \left \{ {{35^{x-1}=35^0} \atop {y=x-2}} \right. \\ \left \{ {{x-1=0} \atop {y=x-2}} \right. \\ \left \{ {{x=1} \atop {y=-1}} \right.$