Sequence problem, Algebra 2 help??

Question

anonymous · Answer

attachment

noseboy908 · Answer

Alright, to the nth term of this sequence, all you have to do is substitute in the n that you're given (7, in this case), and solve for tn. Understand?

anonymous · Answer

whoops, wrong problem, I meant this one....

anonymous · Answer

@sleepyjess :)

noseboy908 · Answer

Alright, so the equation you need to use here is s(n)=[n(a1+an)]/2. So, we need to solve a couple of equations to find a1 and a(n). Know how we do that?

anonymous · Answer

I don't.... These lessons have me so confused honestly

noseboy908 · Answer

No problem. What you must know is that n (or j in this problem) is equal to 28. Now, plug in the first value you'd find, given that j starts at one (Plug in one for j in the given equation right of the Sigma), and plug in 28 for j to find a(n). Tell me what you get please.

sleepyjess · Answer

to find the lower limit you have to plug in 1 for i 
i think

noseboy908 · Answer

Yes. Please find the values I mentioned a moment ago.

anonymous · Answer

plug in one... so that would make it 8(1)-13, right?

anonymous · Answer

so 8-13=-5

noseboy908 · Answer

Yep

noseboy908 · Answer

Now find a(n) please.

anonymous · Answer

how do i do that part?

sleepyjess · Answer

n=28

noseboy908 · Answer

Yep. Plug in 28 for j.

anonymous · Answer

211?

noseboy908 · Answer

Try that again. You're close, but incorrect.

anonymous · Answer

Where do I plug in 28 for J then? I'm confused

noseboy908 · Answer

The same place you plugged the one in before: for j in "8j-13"

anonymous · Answer

8(28)-13 right?

noseboy908 · Answer

Yep. Then plug that in for a(n), and a(1) for a(1) in the equation I gave you. Also, put in n (which is 28), and solve for Sn. Now, I must go, but Sleepless should be able to help if you need more help.

anonymous · Answer

I am still so lost

noseboy908 · Answer

@sleepyjess

noseboy908 · Answer

I'll be back soon, but I have to go for a short while. If sleepless cannot help, I will when I get back.

sleepyjess · Answer

$$s _{n}=[n(a _{1}+a _{n})]/2$$
we know that a1=-5
a28=211
$$s _{28}=[28(-5+211)]/2$$

sleepyjess · Answer

-5+211=206

nipunmalhotra93 · Answer

@maddrea_ you know the formula for the sum of first n natural numbers?

sleepyjess · Answer

[28(206)]/2

nipunmalhotra93 · Answer

$$\sum_{1}^{28}(8i-13)=8\sum_{1}^{28}i-13\sum_{1}^{28}1$$

sleepyjess · Answer

now do 28*206=5768
5768/2=?

anonymous · Answer

Ohhhhh okay, so 2884? That makes more sense now thank you

sleepyjess · Answer

yep if you need any more help just tag me in the question and i will look

anonymous · Answer

Okay I definitely will :)