sequences and series

[hamid14]

it says find the sum of the series :

3 - 6 + 12 - 24 + ... + 3072

I made a formula Sn = 3 * -2 (n-1) and the n-1 is an exponent
but i cant figure out who to get the sum properly. thanks any help is appreciated.

[Insectoid]

Try writing out the first few values to generate a formula.

sum(1) = 3
sum(2) = -3
sum(3) = 9
sum(4) = -15
...

With this information it's relatively straightforward to figure it out.

[hamid14]

lmao sorry but im just not getting this. im actually trying to help someone else.

[RandomLetters]

It's pretty hard to explain how to find the formula.
Use the basic exponential sequence tn = 2^(n-1)

Then

Sn = 2 + 4 + 8 + 16 ... tn

then some magic happens

And you get the formula Sn = a(1 - r^n)/(1-r)

[hamid14]

lol great explanation jk. i got it >.>

[L.mawaty]