Question

Find the 13th partial sum of

Answer 1

118
708
767
1,534

Answer 2

i got 708 am i correct?

Answer 3

@mathmate

Answer 4

I do not see how you got 708, unless I am missing something.

Answer 5

Is it true that the summation goes from i=1 to i=\(\infty\)?

Answer 6

nope

Answer 7

not in this one

Answer 8

But that's what the question says, can you enlarge the question?

Answer 9

i=1 to i=13

Answer 10

first i found a1=6 by substituting 1 in 9i-4

Answer 11

Oh, sorry, I didn't read the text. I just read the image.
Then it should be more than 708.
How did you get 708?

Answer 12

then i found a13=113 by substituting 13 in 9i-4

Answer 13

You can split it up into
\(9\Sigma i\ \ -4\Sigma 1\)

Answer 14

n=(upper limit - lower limit)+1

Answer 15

You can do that too, a13 is correct.
What did you do then?

Answer 16

n(13-1)=12

Answer 17

sn=n/2(a1+an)

Answer 18

n=13 in this case.

Answer 19

What did you get for a1?

Answer 20

a1=6

Answer 21

a1=9*1-4=5 in my books! :)

Answer 22

yup i told u that before in the reply

Answer 23

So do you think a1=5 or a1=6?

Answer 24

a1=5

Answer 25

Good!
So you can apply the formula that you posted earlier
S13=(n/2)(a1+a13)
=?

Answer 26

s13=(13/2)(5+113)

Answer 27

Sounds good to me! What does your calculator tell you for the result?

Answer 28

767

Answer 29

There you go! :) Good work!

Answer 30

can u fan me

Answer 31

For what reason?

Answer 32

so that i can contact u for any other problem that i have in future

Answer 33

You only have to take note of my screen name.
Any time you need help, you include @ mathmate in your text like what you did before.
If I am online and available, I will always come to help you.
I fanned a few persons before, but my screen got very busy when these people come online or offline. So I don't do that any more. Sorry!