Question

Help?

Answer 1

For the first one, it could be a or d. I don't know what n starts on so I don't know.

Answer 2

N is the numbers they provide like -2... thats a1

Answer 3

I was thinking A or D as well. I'm torn because we can only choose one, and only one is correct.

Answer 4

If the index starts at 0, i.e. \(a_0,a_1,a_2,\dots\), then it is pretty clear that it is a. If the index starts at 1, i.e. \(a_1,a_2,a_3,\dots\), then it is pretty clear that it is d. b and c does not make sense since if you increase n by one \(a_n\) would also increase by one. In other words, for b and c, \(a_{n+1}-a_n=1\).

Answer 5

Okay so you're thinking its A? Okay cool how about the next two?

Answer 6

@thomas5267

Answer 7

How do you write down a sequence? Does the index start from 0 or 1?

Answer 8

It starts with 1.

Answer 9

For the write down the explicit definition for the sequence question it should be D.

Answer 10

Yeperonni! thank you!

Answer 11

For the sum of first 10 terms question, use the formula for arithmetic series.

Answer 12

I got C how does that sound?

Answer 13

You missed the factor of 2?

Answer 14

Hang on.

Answer 15

Okay im confused. How do you set this up?

Answer 16

Using \(\displaystyle S_n=\frac{n(a_1+a_n)}{2}\).

Answer 17

S10=10(41+an)/2 ???

Answer 18

That's the general formula. In this case, \(\displaystyle S_{10}=\frac{10(a_1+a_{10})}{2}\)

Answer 19

Ahh okay so B?

Answer 20

Yep.

Answer 21

mm wonder why its not D or C?

Answer 22

Just add the 10 terms manually and you will understand why it is not C or D. XD

Answer 23

AHAHAH oh wow.. missed the sum part. Okay thanks!

Answer 24

For the geometric series, use the formula again.
\[
\sum_{k=0}^nar^k=a\frac{1-r^{n+1}}{1-r}
\]
Note that the sum runs from k=0 to k=n and the it is \(r^{n+1}\) on the numerator of RHS.

Answer 25

I noticed that 0 which makes it 0 right?

Answer 26

???

Answer 27

k-0

Answer 28

Let me just use your formula instead of my teachers.. hang on.

Answer 29

No. \(\displaystyle \sum_{k=0}^nar^k\) means \(ar^0+ar^1+ar^2+\cdots\) all the way up to n.

Answer 30

I seriously dont see how you got that. Im still getting 4.

Answer 31

Yes the answer is 4. Now I am confused on how you got the answer.

Answer 32

BWHAHA thank you anyways!