Question

Help please??
Find S12 for the series 2 + 5 + 8 +...

Answer 1

you do see that it's adding 3 each time so the sequence would be starting from 8 would be. 8, 11, 14, 17, 20, 23, 26, 29, 32. and so on.

Answer 2

So its 35?

Answer 3

ok what is the whole question? cause I just saw that it's adding each number. whats the whole question?

Answer 4

You want to find the sum to the twelfth term.
So you use the formula n/2 * (a + L)

Answer 5

That is the whole question.

Answer 6

this is an arithmetic progression
the first term ,a = 2 and the common difference , d = 3
the nth term is a + (n-1)d the sum of the first n terms is given by n/2(2a + (n-1)d)
The question has S12 so I think it needs the sum not when n= 12 as above.

Answer 7

222

Answer 8

@JackJordan can you explain your formula?

Answer 9

It's standard a-level formula needs no explaining.

Answer 10

So which ones the right answer? I'm kind of confused.

Answer 11

How rude of me. Of course it does... you take the sum of an arithmetic series and another, reverse their order. Add then cancel terms. And you will reach the above formula. Can't fit it here but google "sum of arithmetic series"

Answer 12

The answer is 222. My calculator malfunctioned earlier on.

Answer 13

in all honesty so am I, I never seen this formula before. i'm only in 8th grade

Answer 14

I'm in British College (posh?)... the formula is pretty standard. You can add the numbers up yourself if you want to check.