[m]S_{n}=\frac{2a_{1}+(n-1)d}{2}\cdot n[/m]
n=6
[m]S_{6}=\frac{2a_{1}+5d}{2}\cdot 6[/m]
[m]a_{1}=-11[/m]
[m]S_{6}=\frac{2\cdot (-11)+5\cdot 2,5}{2}\cdot 6[/m]
[m]S_{6}=-28,5[/m]
О т в е т. В)
6.
S_(n)=[m]\frac{b_{1}\cdot (q^{n}-1)}{q-1}[/m]
n=4
b_(1)=2
q=3
S_(4)=[m]\frac{2\cdot (3^{4}-1)}{3-1}[/m]
S_(4)=[m]80[/m]
О т в е т. Г)
7.