Question

Write a formula for the general term (the nth term) of the arithmetic sequence shown below. Do not use a recursion formula. Then use the formula for an to find a20, the 20th term of the sequence.
a1 = -13, d = -5

Answer 1

Answer:

an = a1 + (n-1)*d

a20 = -108

Step-by-step explanation:

For the arithmetic sequence

a1 = -13, d = -5

a2 = a1 +d (where d is the ratio of the sequence)

a2 = -13 -5

a2 = -18

a3 = a2 + d

But a2 = a1 + r

a3 = a1 + 2r = -13 + 2(-5) = -23

So: an = a1 + (n-1)*d

a20 = -13 + 19*(-5)

a20 = -108