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Discrete Math 18 Online
OpenStudy (anonymous):

Find the sum of the geometric sequence.

OpenStudy (anonymous):

1/4, 1/16, 1/64, 1/256

OpenStudy (anonymous):

I don't know where to start

Nnesha (nnesha):

it's geometric sequence firs step to find ratio you can find ratio \[\huge\rm r = \frac{ a_2 }{ a_1} , \frac{ a_4 }{ a_3 }\] divide next term by one previous one to get ratio

Nnesha (nnesha):

there are two formulas to find sum of geometric sequence one is infinite geometric sequence and 2nd one is finite geometric sereies use this formula for infinite geometric when \[\left| r \right| <1\]\[\huge\rm s_n = \frac{ a_1 }{ 1-r }\] and if ratio is greater than then apply this formula finite geometric series \[\huge\rm s_n = a_1 (\frac{ 1 - r^n }{ 1-r })\]

OpenStudy (anonymous):

ok so r= 1/4

Nnesha (nnesha):

yes that's right which is less than one so you suppose to find finite or infinite geometric sum ??

OpenStudy (anonymous):

infinite geometric sum

Nnesha (nnesha):

yep right a_1 first term r= ratio :-) solve that

OpenStudy (anonymous):

ok so 1/1-(1/4) = 4/3? the first term is 1, I accidently started in 1/4

Nnesha (nnesha):

first term is 1 ???

OpenStudy (anonymous):

yes

Nnesha (nnesha):

1/4, 1/16, 1/64, 1/256 first term is what ??

OpenStudy (anonymous):

it goes 1, 1/4, 1/16...

OpenStudy (anonymous):

I typed it in wrong at the beginning. I forgot to put one first

Nnesha (nnesha):

ohh okay

OpenStudy (anonymous):

so what do I do with 4/3 next

Nnesha (nnesha):

\[\huge\rm \frac{ 1 }{ 1 - \frac{ 1 }{ 4 } }\] = 4/3 yes done

OpenStudy (anonymous):

one of the options is 341/256. That's the same thing right?

Nnesha (nnesha):

hmmm not sure what are other options ?

OpenStudy (anonymous):

341 1/192 1/768

Nnesha (nnesha):

yep that's the only one make sense to me

OpenStudy (anonymous):

Yeah it makes sense to me too. Thank you @Nnesha

Nnesha (nnesha):

np :-)

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