Question

Can someone explain to me how to find the answer?
What is the sum of the first 10 terms of the sequence defined by an=3n-3?
A.132
b.138
c.27
d.135

Answer 1

@FortyTheRapper Can you help me?

Answer 2

well N is a term and what else is a term?

Answer 3

um a?

Answer 4

have you covered arithmetic sequences yet?

Answer 5

wait, does is say a n=3n-3 or does it say an=3n-3

Answer 6

Yes, I just dont know how to take it from an equation?

Answer 7

and it says a and a lower in next to it

Answer 8

ok.. one sec

Answer 9

\(\large {\textit{sum of a finite arithmetic sequence}=S_{\color{brown}{ n}}=\cfrac{{\color{brown}{ n}}}{2}(a_1+a_{\color{brown}{ n}})
\\ \quad \\
thus\implies S_{\color{brown}{ 10}}=\cfrac{{\color{brown}{ 10}}}{2}(a_1+a_{\color{brown}{ 10}})
}\)

so.. find the 1st term, and the 10th one, and use them in the SUM equation

Answer 10

\(a_{\color{brown}{ n}}=3{\color{brown}{ n}}-3\qquad
\begin{cases}
a_{\color{brown}{ 1}}=?\\
a_{\color{brown}{ 10}}=?
\end{cases}\)

Answer 11

I don't know what to do....

Answer 12

thought you said you already covered arithmetic sequences

Answer 13

I did, but I'm still not very good at it.

Answer 14

well, the above is very clear, find the 1st and "n"th term, in this case the 10th
and plug them in the SUM equation to get the sum of all 10

Answer 15

I'm sorry.. I'm still not putting two and two together...

Answer 16

that means, you may want to cover your arithmetic sequences section a bit more

Answer 17

Agreed.

Answer 18

but can you help me with this question still?