Question

Please Help! Show me how its done please!
Find the sum of the first 8 terms of the sequence.

1, -3, -7, -11, ...

Answer 1

sooo, you need help adding? or is it that you really need help in determining all the 8 terms?

Answer 2

since the numbers are getting smaller, or going negative, ... and they seem fairly close together. We can try to see if they are subtracting a like amount each time.

Answer 3

Fine out what the term is going up by. I see -4

Answer 4

I need help determining all the 8 terms, this is pre cal and it really confuses me. I'm not sure what formula to use. The Arithmetic Sequence formula?

Answer 5

formulas are only half the battle. seeing a pattern is the key

once you see that pattern, the formula is known by default

Answer 6

So that is it? Its isn't any of the formulas they gave me?

Answer 7

if you subtract 4 from the last term given, what do you get?

Answer 8

-15, -19, -23

Answer 9

.... or if you want to create an expression to use in summation thats fine too

\[\sum_{n=a}^b~a_1+d(n-1)\]
\[\sum_{n=a}^b~a_1+\sum_{n=a}^bd(n-1)\]
\[a_1(b-a)+d\sum_{n=a}^bn-1\]
\[a_1(b-a)+d\sum_{n=a}^bn-d\sum_{n=a}^b1\]
\[a_1(b-a)+d\sum_{n=a}^bn-d(b-a)\]
stuff like that

Answer 10

but yes

..., -15, -19, -23, -27 fill in all 8 terms

Answer 11

\[\frac{n}{2}(a_1+a_8)=sum\]

Answer 12

ok got it! thanks!

Answer 13

youre welcome, good luck :)