Question

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



-110
-116
-122
-128

Answer 1

First, what is your common ratio here?

Answer 2

2?

Answer 3

2? Are you sure? :P

Answer 4

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

Answer 5

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

Answer 6

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

Answer 7

im dont really understand what to do next sorry?

Answer 8

4 - 6 --> -2

Our common difference would be -6 here.

Answer 9

*i

Answer 10

ohh ok

Answer 11

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
\(x_{20} = 4+(20-1)(-6)\)