@kirbykirby

Question

@kirbykirby

anonymous · Answer

$$\sum_{1}^{12}(1+3^i-1)$$

anonymous · Answer

What is the sum of the geometric sequence 1, 3, 9, ... if there are 12 terms?

anonymous · Answer

thats supposed to be 1+3^i-1

kirbykirby · Answer

$$\sum_{1}^{12}(1+3)^{i-1}$$?

anonymous · Answer

292,524

 265,720

 139,968

 104,976


i got 265732

anonymous · Answer

im pretty sure b is correct i was wandering if i entered it wrong or something

kirbykirby · Answer

Is the formula this$$\sum_{1}^{12}(1+3)^{i-1} \text{ or } \sum_{1}^{12}(1+3^{i-1})$$

kirbykirby · Answer

neither of these give a choice in your answers. The 2nd one is closer though to something you have in your answers. Can you be sure there are no typos in the way the formula is written?

anonymous · Answer

the second one is what gave me my answer

kirbykirby · Answer

hm, yes I agree with your answer too :) But it's not in your answer choices. The closest one is  265,720, which is only the result from $ \Large  \sum_{i=1}^{12}3^{i-1}$

anonymous · Answer

i tried todo the next one to see if my calc is off, but its an arithmetic so it gave me a number that was way off

kirbykirby · Answer

no your calculator is not off for the question there..  I tried it myself, and even double checked with wolfram alpha, everything gives 265,732 I am guessing the one who posted this question made some mistake ._.

anonymous · Answer

lol maybe. now i need to see how to solve an arithmetic kind of these lol,

kirbykirby · Answer

hehe ok. Yes there is a different formula for those :)

anonymous · Answer

ok thats what i figured, what website did u find the instructions for?

kirbykirby · Answer

$$\large \begin{align} \sum_{k=1}^n(a+(k-1)d)&=\underbrace{a}_{b_1}+(a+d)+(a+2d)+\ldots+\underbrace{(a+(n-1)d)}_{b_n}\ ~ \ &=\frac{n}{2}\left( 2a+(n-1)d\right) \ ~ \ &=n\left(\frac{b_1+b_n}{2}\right)\end{align} $$

kirbykirby · Answer

it was the texas instruments site

anonymous · Answer

what is d

kirbykirby · Answer

d is the common difference, which you do by taking the 2nd term, and subtract it to the 1st term

kirbykirby · Answer

say you have a sequence like
3, 7, 11, 15

then 7 - 3 = 4, so d = 4

anonymous · Answer

3, 9, 15..., if there are 34 terms?

9-3 = 6 so d= 6

kirbykirby · Answer

yup

anonymous · Answer

our k in this one wouldbe 3?

kirbykirby · Answer

no, here k is the variable. What you need to know are:
$a, d, n$

anonymous · Answer

a=3 d=6 n=34

kirbykirby · Answer

yes

anonymous · Answer

i input it in but again i got an answer that was extremely close like the last one so i chose it.

kirbykirby · Answer

3468?