## anonymous one year ago The first term of an arithmetic sequence is -8 and the common difference is 3. The last term of the sequence is 100. How many terms are there in the sequence? I have been trying to apply a formula that i will post a picture of but its not working, would like some help showing me what to do please!

1. anonymous

the formula I tried: $S _{n}= \frac{ 1 }{ 2 }n \left[ 2a +(n-1)d \right]$

2. anonymous

Here was me trying it

3. anonymous

4. anonymous

i got answer for this but different method

5. anonymous

I am learning from my textbook and I am pretty sure they want me to use that method to find it since it was in the example, but I am open to learning a different one! The answer is 37.

6. anonymous

great let me show you the way @Zas

7. anonymous

so thing you used there - the a+(n-1)d - that will always work for this type of question?

8. anonymous

yeah wait i will explain when to use the formula you gave earlier

9. anonymous

Because I also think that they actually wanted me to use that and I was just doing the wrong thing :)

10. anonymous

Ok

11. anonymous

a simple example to show it uses ^_^ hope helps you to understand well

12. anonymous

Oh I see, I just used the wrong one didn't I? Oh well, than you very much!

13. anonymous

no problem im glad i helped you with that question ^_^ dont worry you just need a lot exercise more