7х+у=20
у=20-7х
у=13
13+7х=20
20=20
Ответ:у=20
х-5у=8
х+5у=8
х=13
13-5у=8
8=8
Ответ:х=13
1) ab(3a-b-a+2b) = ab(2a+b)2)mn(1-7n-1-7n) = -14mn^23) xy(10y-10+y) = xy(11y-10)<span>4)xz(5z-4x+1-5z) = xz(1-4x)</span>
= (5*1,5)*а^6-2*a+(-4a^5)+a^4+36=7,5*а^6-2*a+(-4a^5)+a^4+36= 7,5*а^6--4a^5+a^4-2*a+36=a(7,5a^5-4a^4+a^3-2)+36