arithmetic Sequence: (2, 4, 8, 16....)
number of times is 10.
Need: an=a1+(n-1)d
also need the sum: Sn=n/2(a1+an)
Help? I'm stuck.

Question

arithmetic Sequence: (2, 4, 8, 16....)
number of times is 10.
Need: an=a1+(n-1)d
also need the sum: Sn=n/2(a1+an)
Help? I'm stuck.

anonymous · Answer

Do you have a1 yet?

anonymous · Answer

a1 should be 2 since its the first term

anonymous · Answer

its "d" that I am having a problem with....

anonymous · Answer

Yep, do you have difference d yet?

anonymous · Answer

if you take 4 -2 =2.....doesn't work for the total problem

anonymous · Answer

I believe it's not arithmetic!

anonymous · Answer

its either arithmetic or geometric sequence...since this is the worksheet that I am working on

anonymous · Answer

It's obviously geometric!
Can you find ratio r?

anonymous · Answer

Ok, haven't learned this part yet....but you can explain it and I'll be ahead for Monday's class!!!! LOL

anonymous · Answer

If you want...or I can wait til Monday!

anonymous · Answer

Instead of subtract, now you divide r = 4/2 = 8/4 = ...

anonymous · Answer

and the rest of the formula is the same???

anonymous · Answer

a_10 = a_1 * r^ 9

anonymous · Answer

ok, thanks for your help...I better wait til Monday for this problem to see how my professor wants us to work this type...Thanks Again!!!

anonymous · Answer

:)