Question

Find the 11th term of the arithmetic sequence. a_3 = 20.5 and a_8 = 13, a_11 = ______.

Answer 1

Could you show us wat you've done so far with the question please?

Answer 2

i dont know how to do it

Answer 3

a_8 = (a_3) + 5d

13 = 20.5 + 5d

solve for d

Answer 4

Okay, well, let's start wiht the formula of an arithmetic sequence. what's the formula?

Answer 5

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

Answer 6

Okay, let's have this arithmetic sequence:
\[a_{1}+(a_{1}+d)+(a_{1}+2d)+(a_{1}+3d)...\]

Answer 7

AS you keep going up to the 8th term, what would the expression be for the 8th term?

Answer 8

So basically what would:
\[a_{8}=?\]
Using your formula for an arithmetic sequence in terms of a and d?

Answer 9

@tomtom777 Are you there?

Answer 10

hello @Azteck sorry i had dinner and idk understand

Answer 11

What do you mean? You just substitute n with 8 and get an expression in terms of a and d.

Answer 12

what about a1

Answer 13

Does not matter. it will cancel out afterwards.

Answer 14

a1 or a. it's the same thing.

Answer 15

The formula can be written as this:
\[T_{n}=a+(n-1)d\]

Answer 16

I'm used to it being written as that, so you might have to adapt or just use common sense that when I say a it means a_{1} etc. ;)

Answer 17

can u just solve it

Answer 18

@Azteck

Answer 19

I'm not going to gain anything, you're not going to gain anything. Wouldn't it be better to not ask about the question at all if you want us to do the question for you? We're here to HELP and GUIDE you so that you know how to do it and everybody will be happy.

Answer 20

So you know the formula for an arithmetic term.
\[T_{n}=a+(n-1)d\]
What would T_{8} be?
\[T_{8}=a+(8-1)d\]