(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^(-7) * 3^9 = 3^(-7+9) = 3^2
2)3^2/3^4 = 3^(2-4) = 3^(-2)
a8=a1+7d=60
a7/a1=a25/a7=q
a1=60-d
a7=60-d+6d=60+5d
a25=60-d+24d=60+23d
d не равно 0 по условию, значит d=15
a1=60-15=45
a7=60+5*15=60+75=135
q=a7/a1=135/45=3
{х+2у+2у=11
{<span>5х-3у=3
</span><span>{х+4у=11 /х3
</span><span>{5х-3у=3 /х4
</span><span>{3х+12у=33
</span>20х-12у=12
23х=45
х=45/23
5(45/23)-3у=3
225/23-3у=3
-3у=3-225/23
-3у=-156/23
3у=156/23
у=52/23