Question

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!

Answer 1

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

Answer 2

Here was me trying it

Answer 3

do you have answer?

Answer 4

i got answer for this but different method

Answer 5

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.

Answer 6

great let me show you the way @Zas

Answer 7

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

Answer 8

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

Answer 9

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

Answer 10

Ok

Answer 11

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

Answer 12

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

Answer 13

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