Объяснение:

1.

[tex]b_1=-15\ \ \ \ q=3\ \ \ \ b_9=?\\\\\boxed {b_n=b_1q^{n-1}}\ \ \ \ \Rightarrow\\\\b_9=-15*3^{9-1}=-15*3^8=-15*6561=-98415.[/tex]

2.

[tex]a_{12}=36\ \ \ \ d=3\ \ \ \ S_{12}=?\\\\\boxed{a_n=a_1+(n-1)d}\ \ \ \ \Rightarrow\\\\a_{12}=a_1+(12-1)d\\\\36=a_1+11*3\\\\\displaystyle\\36=a_1+33\\\\a_1=3.\\\\S_{n}=\frac{a_1+a_n}{2}n \\\\S_{12}=\frac{3+36}{2}*12=39*6=234.[/tex]

3.

[tex]b_8=40\ \ \ \ q=2\ \ \ \ S_{10}=?\\\\b_8=b_1*q^7\\\\40=b_1*2^7\\\\40=128b_1\ |:128\\\\b_1=\frac{5}{16} \\\\\boxed{S_n=b_1*\frac{q^n-1}{q-1}} \\\\\displaystyle\\S_{10}=\frac{5}{16} *\frac{2^{10}-1}{2-1} =\frac{5}{16}*\frac{1024-1}{1}= \frac{5}{16}*1023=\frac{5115}{16} =319\frac{11}{16} .[/tex]