Answer:
1) Second option: -3
2) Second option: 183
Step-by-step explanation:
1) You can use any two consecutive terms to find the common ratio. This is given by:
[tex]r=\frac{a_n}{a_{n-1}}[/tex]
You can choose these consecutive terms:
[tex]a_n=-9\\a_{n-1}=3[/tex]
Then the common ratio "r" is:
[tex]r=\frac{-9}{3}=-3[/tex]
2) The sum of the first "n" terms can be found with this formula:
[tex]S_n=\frac{a_1(r^n-1)}{r-1}[/tex]
Since ther first term is 3 and you need to find the sum of the first 5 terms, then:
[tex]a_1=3\\n=5[/tex]
Substituting into [tex]Sn=\frac{a_1(r^n-1)}{r-1}[/tex], you get:
[tex]S_{(5)}=\frac{3((-3)^5-1)}{-3-1}=183[/tex]
