(12-2а)/4 - (1-5а)/5 >0,
5(6-a)-2(1-5a)>0,
30-5a-2+10a>0,
5a>-28,
a>-5,6;
a=-5;
(а/с - 2 + с/а)*10/(а-с) = (a^2-2ac+c^2)/(ac) * 10/(a-c) = (a-c)^2/(ac) * 10/(a-c) = (a-c)/(ac) * 10=10(a-c)/(ac),
10(a-c)/(ac)=10(5-(1))/(5*(-1))=10(5+1)/(-5)=-60/5=-12.
(-1/3)² *2-1/3+3=1/9*2-1/3+3=26/9
6-у + 36 - у²=42-y-y²=<u>(6-y)(y+7)</u>
X-y=3 | -3
3x-y=13
-3x+3y=-9
3x+3y=-9
________
-3x+3y+3x+3y=-9-9
-3x и 3x - зачеркиваем.
3y+3y=-18
6y=-18
y=-3