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CLEARLY stated:If I know that a1 + a2 is 13

And a4 is -1

How can I get sum number of first 30 numbers in sequence?

We have an arithmetic sequence.

Sum of first 2 terms = 13

4th term = -1

Go here :

Sal introduces arithmetic sequences and their main features, the initial term and the common difference. He gives various examples of such sequences, defined explicitly and recursively.

www.khanacademy.org

Come back if you have questions.

We're given that \(a_4 = -1\) but we're not told a common difference. Hmm... well, the most important principle in all of algebra is that if we don't know a value, we can give that value a name so as to make talking about it and working with it easier. Let \(d\) be the common difference of the sequence \(a_n\). Can you see why that means we can say that \(a_4 = a_3 + d \implies -1 = a_3 + d\)? How can you rearrange that equation such that we have \(a_3 = (\text{something})\)? Using this result, what can you say about \(a_2\)? And then what can you say about \(a_1\)? Finally, what do you get when you plug these values into the first given equation that \(a_1 + a_2 = 13\)? Where does that lead you?

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a1 + a2 is 13 translates into (aHi,

If I know that a1 + a2 is 13

And a4 is -1

How can I get sum number of first 30 numbers in sequence?

Is there any online calculator that can help me?

Now a

Now solve 2a

Can you finish from here?

Last edited:

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No no, only Subhotosh can recommend such videos. You can get into great trouble doing this. No need to worry as ICLEARLY stated:

We have an arithmetic sequence.

Sum of first 2 terms = 13

4th term = -1

Go here :

## Intro to arithmetic sequences

Sal introduces arithmetic sequences and their main features, the initial term and the common difference. He gives various examples of such sequences, defined explicitly and recursively.www.khanacademy.org

Come back if you have questions.

BTW would you be interested in purchasing a bridge I have for sale, it's called the Brooklyn Bridge

HOKAY: a dollar down and a dollar a week;BTW would you be interested in purchasing a bridge I have for sale, it's called the Brooklyn Bridge

I'll have my people contact your people...

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People who need a calculator do not know. You Makito want to know.If I know that a1 + a2 is 13

And a4 is -1

How can I get sum number of first 30 numbers in sequence?

Arithmetic series have only two essential parts: a first term and a common different.

Suppose that the first term is \(\displaystyle a_1\) and a common different is \(\displaystyle d\).

Then the sequence is \(\displaystyle a_n=a_1+ [(n-1)d]\)

Now the sum \(\displaystyle {S_n} = \sum\limits_{k = 1}^n {{a_1}(k - 1)d} = {a_1}d\sum\limits_{k = 1}^n {(k - 1)} = {a_1}d\frac{{(n - 1)n}}{2} \)

If \(\displaystyle a_1+a_2=13\) then \(\displaystyle a_1+(a_1+d)=13 \text{ or }2a_1+d=13\)

Now Show us what you can do with his help!