Question

Sequences: Find a formula for S_n where n is greater or equal to 1:
1,3,7,15,31......

Answer 1

easy it is pippa i expect u to solve this :P

Answer 2

well i never learnt this in my life

Answer 3

first time i am touching upon it lol

Answer 4

i know there is (4)^n

Answer 5

thatt i see plus the previous term

Answer 6

c in each sequence the difference is getting multiplied by 2
like there is diff of 2 between 1 and 3
diff of 4 btw 3 and 7
and so

Answer 7

lol i was totally offf heheheh

Answer 8

okk i see that

Answer 9

did u got the sequence now

Answer 10

so like how wld i set up the formula?

Answer 11

The nth term is (2^n) - 1. Now, the sum ....:)

Answer 12

y -1?

Answer 13

pippa n is the term for which we have to find
like first term means n=1

Answer 14

ya i get that

Answer 15

still a drop confused lol

Answer 16

good dumbo :P

Answer 17

Thanks smarty pants :D

Answer 18

ghost can u explain to me

Answer 19

hahaha ok i see it thanks ghost

Answer 20

The sum of the first n terms where n is a positve integer can be found by the partial sum formula 2^ (n+1) - ( n + 2). Check it, please.

Answer 21

but the first one u gave made sense

Answer 22

That was for a particular term. Say, you wanted to know the 8th term in the sequence.

It would be (2^n) - 1 evaluated fo n = 8. So, the 8th term is 2^8 - 1 = 255.

Answer 23

right ok

Answer 24

so y did u give me this other formula?

Answer 25

2^(8 +1) - (8+2) = 2^9 - 10 = 502.

Answer 26

ohhh

Answer 27

like how am i supposed to figure that out on my own? is there a process?

Answer 28

ohh but i dont think it wants the addition of all th eterms it just wants like to find liek n terms

Answer 29

The sum of the entire series does not exist. The partial sum formula does.Partial means for a finite number of terms.

Answer 30

i dont think they r referring to that fance formula i think they only want me to give the simple one

Answer 31

Now, the sum of the first 8 terms (1 + 3 + 7 + 15 + 31 + 63 + 127 + 255 = 502) should be the partial sum formula *** 2^ (n+1) - ( n + 2) *** evaluated for 8.

Answer 32

ya but i dont think i need the sum.

Answer 33

Find a formula for S_n. S sub n *means* the sum of the first n terms, I think. I had an arithmetic error in my formula check. All's well.

Answer 34

thanks ghost,i have anotehr one of these but will post it on anotehr thread

Answer 35

Okay.