Question

What is the sum of a 7-term geometric series if the first term is -11, the last term is -45,056, and the common ratio is -4?

-143,231
-36,047
144,177
716,144

Answer 1

I had to refersh sorry

Answer 2

\(\large\color{black}{ S_n=\frac{\LARGE a_1(1-r^n)}{\LARGE 1-r}}\)

Answer 3

What would n be?

Answer 4

you know that:
~ \(\large\color{black}{ a_1 =-11}\)
~ \(\large\color{black}{ r =-4}\)
~ \(\large\color{black}{ n =7}\)
~ \(\large\color{black}{ S_n =S_7}\)

Answer 5

-36,047

Answer 6

that is the sum?

Answer 7

Wouldn't it be B because if you fill out the equation and find the answer I got -36.047

Answer 8

I'll check this

Answer 9

\(\large\color{black}{ S_n=\frac{\LARGE (-11)(1-(-4)^7)}{\LARGE 1-7}}\)

\(\large\color{black}{ S_n=\frac{\LARGE (-11)(1+4^7)}{\LARGE 6}}\)

Answer 10

6 is negtative

Answer 11

(-11)(1+4^7)/-6

Answer 12

(11)(1+4^7)/6

Answer 13

Hitn: they give you the last term: -45,056

Answer 14

r=-4 so if you put 1-r it would turn into 1+4 meaning divide by +5 right?

Answer 15

you don't need the 7th term for the sum