Question

Identify the 35th term of an arithmetic sequence where a1 = -7 and a18 = 95

Answer 1

@iGreen

Answer 2

do you use the Sn=n/2(a1+an) that's what I am doing but i cant get the right answer....

Answer 3

is it 198 and 1/3?

Answer 4

@cerickson2 , you are using a sum formula to attempt to find a specific value of the sequence. What you want to do in order to find this out is to use a different formula, one moment.

Answer 5

How would you do that?

Answer 6

@msasu25 the answer choices are
203
197
168
163

Answer 7

The formula for finding any term of a given arithmetic sequence is: \[a_{n}=a_{1}+(n-1)d\]What you need to do, first off, is use your two given term and given n to solve for d.

Use the term wth n_18 as your a-sub-n, and use the term with the lower n as your a-sub-1.

Answer 8

what numbers are used in which places?

Answer 9

\[a_{n}=a_{1}+(n-1)d, \ \text{where}\]\[a_{n}=a_{18}=95; \ \ \ a_{1}=-7; \ \ \ n=18; \ \ \ d= \ ?\]

Answer 10

so it would look like
a18 = -7 +(18 - 1) d
??????

Answer 11

Correct! Solve for n, when you have 95 on the other side of the equation.

Answer 12

wait, where would 95 go?

Answer 13

a18=-7+(18-1)d
a18=-7+(17)d
a18=10d
I dont know what to do next

Answer 14

I don't think you can add the -7 to the 17d

Answer 15

oh... hah then what would i do?

Answer 16

I have no idea lol

Answer 17

thats ok

@Mendicant_Bias

Answer 18

I think you don't understand how equations work, one moment.

Answer 19

I mean the 95 would go on the lhs then add 7 to both sides

Answer 20

ok I got the answer now

Answer 21

@cerickson2 , could you take a shot at writing out what the equation looks like to you, without any values? Just variables?

Answer 22

what do you mean...?

Answer 23

like in words, say nth term = first term + (blahl balh)

Answer 24

Not even in words, with symbols.

Answer 25

actually first write out an arithmetic sequence 3 + 5 + 7 + 9 + 11

Answer 26

I gave you an equation, can you write it down, without numbers, again?

Answer 27

no idea how....

Answer 28

You use symbols, like this:

a_1+a_2=n+d+blahblahblah

Answer 29

do you know the definition of an arithmetic sequence?

Answer 30

no

Answer 31

I used symbols, to describe a relationship between numbers. That's what an equation is, cerickson.

Answer 32

ok you need to start there

Answer 33

Hold off on the arithmetic sequence stuff. He needs to at least understand what functions and equations are first.

Answer 34

provide an example of an arithmetic sequence

Answer 35

i guess, ok gl guys

Answer 36

But yeah, make me a fictional equation, @cerickson2 , just make one up, doesn't matter what it is. Can you do that? Just make a relationship between a bunch of symbols.

Answer 37

can you give me an example cause you lost me a long time ago...

Answer 38

\[5+a=b\]

Answer 39

That is an example of an equation. That is what an equation is.

Answer 40

can you just make up a problem just like the one I have a question on. All I need is to see how to do a similar problem and then Ill figure it out...

Answer 41

I'll do that, but there's a few things you have to do first. I give you my word you'll both get your answer and understand how it works.

Could you make up an equation and give me an example of it? An equation is a relation between a bunch of things that has an equals sign in the middle. Can you do that?

Answer 42

like 35+1*x=72 ....like that?

Answer 43

Exactly! Excellent, awesome! That is an equation. Great.

Alright, so I gave you an equation that describes how an arithmetic series works, but @msasu25 had a good idea in that he asked you to try to write out an arithmetic sequence, could you do that? It's okay if you can't, but take a shot at it, and if not, I'll show you how.

Answer 44

yeah... I wouldnt know how to do that

Answer 45

Alright, no problem. Here's some examples of arithmetic series:
\[S = 2, \ 4,\ 6,\ 8,\ 10,\ \dots\]
\[S = 1, \ 3, \ 5, \ 7, \ 9 \dots\]
\[S=5, \ 10, \ 15, \ 20, \ 25, \ \dots\]

Answer 46

Alright, I'll be right back, but I have to go.

Answer 47

~15 minutes.

Answer 48

whats the answer to my question though.... i dont have time... Ill find someone else.......

Answer 49

I have to go to an advising appointment, if you're asking for answers for a test or homework that is due today, I cannot help you other than teaching you how to do it and helping you get to the answer.

Actually, I'll give it to you, as long as you come back and learn how to do it, okay?

Answer 50

Does that sound good, @cerickson2 ?

Answer 51

yes! I would love to learn how to do it

Answer 52

Alright, your answer is 197.

Answer 53

Good luck, and I'll be back later.

Answer 54

thank you. Ill keep the question open so when you get back you can teach me

Answer 55

file://localhost/Users/sylvanerickson/Pictures/Photo%20Booth/Photo%20on%202014-12-11%20at%2010.42.jpg

Answer 56

its a different problem but my boyfriend helped me.

Answer 57

Your file is hosted on your computer, I can't connect to that, but sure thing, it's good that you figured it out!