Question

Find the sum of a finite arithmetic sequence from n = 1 to n = 15, using the expression 2n + 5
315

215

32

35

Answer 1

@jdoe0001

Answer 2

Oh so someone is helping you already?

Answer 3

You could help too xD the more the better c: Because im just as confused..

Answer 4

Confused?? Where??

Answer 5

Everywhere. LOL

Answer 6

IVe done this 8 times, and i still dont get it.

Answer 7

You have given, n = 1 from 15 and you have got one expression too..

Start by putting n = 1 in that expression.. Can you do this?

Answer 8

You have : 2n + 5 here just put n = 1 and tell me what do you get?

Answer 9

7.

Answer 10

And similarly, put 2..

Answer 11

i have to do this 15 times? ;-;

Answer 12

No, after 2 just one more time..

Answer 13

Okay, so 7,9,11

Answer 14

Oh wait, ;o

Answer 15

I have asked to do only for 2, as you have done for 3 too, so its your mistake, now you will do for n = 15, you yourself have increased your work.. :P

Answer 16

i go 315 :D Well, its easier for me.

Answer 17

You have solved it??

Answer 18

Yeah, it isnt that hard o-o one i found the first 3, i found the pattern. then i continued it up to 15, then i added.

Answer 19

n=15*

Answer 20

Hey, you have to do this with using Arithmetic Progression, not by simply adding them one by one.. :)

Answer 21

Well, i did get it right xD

Answer 22

Yes, it is maths, this is its beauty that you get same answer but yet different ways are there to do that, and you must do in the way the question is asking you to do as.. :)

Answer 23

Yeah, thats the confusing way xD

Answer 24

hmmm did you find it?

Answer 25

\(\bf a_1=2(1)+5\to 9\qquad a_{15}=2(15)+5\to 35
\\ \quad \\
S_{\color{brown}{ n}}=\cfrac{{\color{brown}{ n}}}{2}a_1+a_{\color{brown}{ n}}\implies S_{\color{brown}{ 15}}=\cfrac{{\color{brown}{ 15}}}{2}a_1+a_{\color{brown}{ 15}}\)