Question

I don't know what to do

find the nth term of each arithmetic sequence described.
-9, -7, -5, -3, ...for n=18

Answer 1

Just use this fomular
nth = a +(n-1)*d

Answer 2

"the nth, or last, term of an arithmetic sequence equals the first term plus (n-1) times the spacing between terms (d)."

What is d, the spacing between terms? How big is the jump from -9 to -7?

Answer 3

2

Answer 4

n is the index, or counter, of the terms. You could say, "seventh term" and let n = 7 represent that.

Answer 5

yes, "d" is 2.

Answer 6

What's the first term, a?

Answer 7

They all add up to 2

Answer 8

The given sequence is -9, -7, -5, -3, ..
What is the first term of this arithmetic sequence?

That's "a". Answer this, please: a = ?

Answer 9

a is 2

Answer 10

Actually, "d" is 2. "d" is the jump from one term of the sequence to the next. You were right on that. But look at the sequence: -9, -7, -5, -3, ..
What is the first term of this sequence?

Answer 11

-9

Answer 12

That's correct.
Look at what we have now: a = -9
d = 2
n = 18

Please calculate (n-1). n-1 = ?

Answer 13

Again: nth term of arith sequence = first term of sequence plus (n-1)* jump

\[a _{n}=a _{1}+(n-1)d\]

Answer 14

What is

18
- 1
-------- ??

Answer 15

17

Answer 16

Don't you do distributive property???

Answer 17

You could, but it's easier simply to recognize that 18-1=17 and then multiply this (n-1) by d, or to multiply this 17 by 2. What is 17 * 2?

Answer 18

34

Answer 19

And the first term is -9.

The 18th term is then -9 + 34.

Please calculate this.

Answer 20

\[a _{18}=-9+34=?\]

Answer 21

Why is it a18 and not -9???

Answer 22

Got 25 btw