What is the 20th term of the arithmetic sequence 4, -2, -8, ... ? :p

-110
-116
-122
-128

Question

What is the 20th term of the arithmetic sequence 4, -2, -8, ... ? :p



-110
-116
-122
-128

zepp · Answer

First, what is your common ratio here?

anonymous · Answer

2?

zepp · Answer

2? Are you sure? :P

zepp · Answer

What did you we do to 4 so it becomes a -2?

anonymous · Answer

if this is arithmetic, shouldn't it be common difference?

zepp · Answer

Oh, right :( I just like the term 'common ratio' too much :U

anonymous · Answer

im dont really understand what to do next sorry?

zepp · Answer

4 - 6 --> -2

Our common difference would be -6 here.

anonymous · Answer

*i

anonymous · Answer

ohh ok

zepp · Answer

The use the formula
$x_n = a+(n-1)d$

Where $x_n$ is what you are looking for;
a the first term;
n the term you are looking for;
d the common difference.

We want the 20th, let n be 20
$x_{20} = a+(20-1)d$
And plug in everything else
$x_{20} = 4+(20-1)(-6)$