Question

Find

Answer 1

\[a _{n} \]

Answer 2

and \[a_{8}\]

Answer 3

lol try a complete sentence with out hitting post

Answer 4

where \[a_{12 = 60}\] and \[a_{20= 84}\]

Answer 5

Yeah sorry for writing one by one.. lol

Answer 6

are we assuming the sequence is geometric?

Answer 7

idk

Answer 8

I dont think there is enough information to answer this, but I could be wrong

Answer 9

oh my bad, it says find\[a_{1}\] for each arithmetic sequence

Answer 10

does it show you what a is?

Answer 11

Nah, you don't need to, it's an arithmetic sequence. You can solve it directly.

Answer 12

no but a12=60 and a20=84 is given

Answer 13

@LolWolf How do you do this?

Answer 14

May I, @zzr0ck3r ?

Answer 15

i guess he left.

Answer 16

lol of course:) I dont think I understand the question

Answer 17

Find a1 for the arithmetic sequence
\[a_{_{12}} = 60 \] \[a_{_{20}} = 84 \]

Answer 18

Okay this is what i can get out of the whole mess....

Answer 19

All right, since the series is arithmetic, we have that \(a_n\) must be of the form:
\[
a_n=kn+b
\]For some \(k, b\). So, we can find \(k\) by using:
\[
k=\frac{a_{l}-a_m}{l-m}
\]Which means:
\[
k=\frac{84-60}{20-12}=\frac{24}{8}=3
\]So, we have that \(k=3\), plugging this in:
\[
a_n=3n+b
\]Now, to find \(b\):
\[\begin{align}
a_{12}&=60=3(12)+b\implies\\
60&=36+b\implies\\
b&=24
\end{align}
\]Therefore, just to check:
\[
a_{20}=3(20)+24=60+24=84
\]As said, so we are correct.
So, we can simply plug in:
\[
a_n=3n+24\\
a_1=3(1)+24=27
\]

Answer 20

Et voilá!