А) (12ав-5а)-(ав+6а)=12ав-5а-ав-6а=11ав-11а=11а(в-1)
б)
В)
Г) 10
A8=a1+7d
a1=a8-7d=-26-7*(-2)=-26+14=-12
S12=<u>2a1+d(12-1)</u> *12=( 2*(-12)-2*11)*6= (-24-22)*6=-46*6=-276.<u>
</u> 2<u>
</u>
[x²(x-3)-(x-3)]/[(x+1)(x+2)]>0
(x-3)(x²-1)/(x+1)(x+2)]>0
(x-3)(x-1)(x+1)/[(x+1)(x+2)]>0
(x-3)(x-1)/(x+2)>0,x≠-1
x=3 x=1 x=-2
_ + + _ +
--------(2) ---------(-1)-----------(1)----------(3)-----------
x∈(-2;-1) U (-1;1) U (3;∞)
Г)162!!x1^3+x2^3=(x1+x2)((x1+x2)^2-3x1x2)
x1+x2=-b=-3
x1x2=c=-15