2х+у=7 ⇒ y=7-2x ⇒ y=7-2x ⇒ y=7-2x ⇒y=7-6=1
х-2у=1 x-2(7-2x)=1 x-14+4x-1=0 5x=15 x=3
Х+m-2(x-m)=6
2x-m-2(3x+2m)=-78
x+m-2x+2m=6
2x-m-6x-4m=-78
-x+3m=6
-4x-5m=-78
x=3m-6
-4(3m-6)-5m=-78
-12m+24-5m=-78
-17m=-78-24
-17m=-102
m=6 x =3*6-6=12
2(m+n)....................
Log9 (27c) =log3 (27c) / log3 (9) = (log3 (27) + log3 (c)) / 2 = (3 +0.5) / 2=3.5/2=1,75
-2,3(82)= -2+(382-3)/990= -2 целых и 379/990