Решите пж системы, сегодня нужно 1) lgx-lgy=2 x-10y=900 2) lgx-lgy=7 lgx+lgy=5

1) $\left \{ {{lg(x/y)=2} \atop {x-10y=900}} \right.$
$\left \{ {{x/y=100} \atop {x-10y=900}} \right.$
$\left \{ {{x=100y} \atop {x-10y=900}} \right.$
100y-10y=900
90y=900
y=10
x=1000

2) $\left \{ {{lg(x/y)=7} \atop {lg(xy)=5}} \right.$
$\left \{ {{x/y=7} \atop {xy=5}} \right.$
$\left \{ {{x=7y} \atop {xy=5}} \right.$
7y^2=5
y^2=5/7
y=+-\sqrt{5/7}
y1=sqrt(5/7), x1=7sqrt(5/7)
y2=-sqrt(5/7), x2=-7sqrt(5/7)