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|dw:1362285707700:dw|\[\Sigma \]

Find the sum of the arithmetic series! Pleassse help:)

Where r we getting this formula? I'm confused where to start

thats a standard formula that can be used.

do you want a formula for sum of terms in arithmetic series ? its equivalent to this formula

Deriving the formula for an arithmetic series?

Yes that is the formula for the arithmetic series. Where do we go from there?:)

to find the sum?

So anyway, this sum is just...
|dw:1362286375802:dw|
right?

terenzreignz...how do you get these expanded form answer? Can u explain that? sorry

It is isn't the right answer in the back of the book

\[\huge \sum_{k=1}^nk=1+2+3+...+(n-1)+n\]
Bloody typo, sorry :)

So anyway, we can rearrange...|dw:1362286994735:dw|

And notice that these terms...|dw:1362287037927:dw|
When added, they all equal n+1

what is the final answer? the answer is supposed to be 25,250...I just don't know how to get it

did you try any one of the 2 formula i gave u ??

Anyone?

So i fill in that question mark spot with 100?
Im not sure

general term =5k
with k=100, last term = 5*100 = 500
-_-

To clarify, this is the formula I am using.
\[S _{n}=\frac{ n(t _{1}+ t _{n} )}{ 2 }\]

wait how does k =100 again?

lower limit givs first term, upper limit gives last term

ok so 100 is the last term... And why do we multiply it by 5?

last value of k is 100
general term = 5k
so last term = 5*100

and the difference between the numbers would be five right? or is it something else

Oh ok that makes sense now. Maybe you should help me on other problems I post. Your a good help!

ok, sure, but did u get 25250 for this one ?

Oh wait quick question! What was \[t _{1}\] in this equation

t1 is the 1st term
index represents which term

tn is the n'th term

the index is which part again?

so t1 is 5

yup. as 5 is the 1st term

any more doubts ?

oh wait my bad! i got it

you mean in \(S_n = n (t_1+t_n)/2\)
thats a general formula, do you want a derivation of this ?

oh u got it ? good :)

|dw:1362289579021:dw|
Like this. N does not equal 1

i think u have made up this question ? or is it from your book/notes ?

I made it up

here Ill give you one from the book.
|dw:1362289721775:dw|

thats 30- m by the way. It kinda got cut off

so, here your 1st term will start from m=10 in 30-m
and last term you'll get by putting m=20 in 30-m

so how would i get
\[t _{n}\]

tm = last term, last m =30
so to get last term tm, put m=30 in general term 30-m
is this confusing ?

kinda

general term tm =30-m
fist term t10 = 30-10 (put m=10)
last term t20 = 30-20 (put m=20)

so I would do 30 -10 first , and when do I do the 20? i dont know if that makes sense

it doesn't -_-

ok lets not do this problem.. Ill ask my teacher on monday..

Ill be posting other problems so u may help me if u want