9514 1404 393
Answer:
17. an = 4 +7(n -1)
18. an = 35 -4(n -1)
19. an = 21 +6(n -1)
20. an = 2 +5(n -1)
Step-by-step explanation:
There are two numbers that tell you everything you need to know about an arithmetic sequence:
- the first term (a1)
- the common difference (d)
Using these two numbers, you can write the expression for the n-th term of the sequence as ...
an = a1 + d(n -1)
This is true for any arithmetic sequence.
__
The first term is the first one listed, so is not hard to find.
The common difference is the difference between the second term and the first term: d = a2 -a1. Usually, you can do this subtraction in your head, so "by inspection" you can find the first term and common difference. For example, in problem 17, it is d = 11 -4 = 7.
_____
17. an = 4 +7(n -1)
18. an = 35 -4(n -1)
19. an = 21 +6(n -1)
20. an = 2 +5(n -1)
