-3x²-12x-12=x²+4x+4=(x+2)(x+2)
{a}- ар. пр.
S(6)= (a(1) + a(5))/2 * 5=
a(5)= a(1) + 4 d
d=a(2) - a(1) = -1.2 - (-6.2) = 5
a(5)= -6.2 + 4*5 = 13.8
S(6)= (-6.2 + 13.8.)/2 *5= (7.6/2)*5= 19
3/2; 3/4; 3/8 ...
q=(3/4)*(3/2)=1/2
Sn=b₁/(1-q)=(3/2)/(1-(1/2))=(3/2)/(1/2)=3.
Ответ: Sn=3.