Question

How do I solve this problem, I am not supposed to use the recursion formulaThen I need to use the formula for an to find a20

Answer 1

To answer this question, we can use the explicit formula of an arithmetic sequence:

`a_n=a_1+(n-1)d`

• We have that the first term (a1) of the arithmetic sequence is 6 (a1 = 6).

,

• The common difference is 3 (d = 3).

Then, we have that the formula is:

`a_n=6+(n-1)\cdot3=6+3(n-1)`

We can use this formula to find the 20th term of this arithmetic sequence as follows:

`a_(20)=6+3\cdot(20-1)=6+3\cdot(19)=6+57=63\Rightarrow a_(20)=63`

In summary, the formula for the arithmetic sequence is:

`a_n=6+3(n-1)`

And the 20th term is equal to 63.