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Mathematics 7 Online
OpenStudy (adryin):

Will fan!

OpenStudy (alones.):

Like what dear?

OpenStudy (adryin):

https://imgbomb.com/i/?KZVdx

OpenStudy (adryin):

All of these seem to have an infinite sum

OpenStudy (adryin):

I need to find which of these equations is a convergent series

OpenStudy (alones.):

Hrmm Im not actually sure :#

jimthompson5910 (jim_thompson5910):

each series is a geometric series. Hopefully you agree with that statement and see why?

jimthompson5910 (jim_thompson5910):

sorry C isn't geometric

OpenStudy (adryin):

Isnt C arithmetic?

jimthompson5910 (jim_thompson5910):

yes it is, my bad

OpenStudy (adryin):

I need to find which one of these is a convergent series.

jimthompson5910 (jim_thompson5910):

the three trailing dots imply that the series goes on forever

OpenStudy (adryin):

I know

jimthompson5910 (jim_thompson5910):

with geometric series, the infinite series only converges if and only if |r| < 1

OpenStudy (adryin):

Yes but the ratio for all of them except a have a ratio greater then 1 for me

jimthompson5910 (jim_thompson5910):

for example, B will not converge because r = 3 in this case and r = 3 makes |r| < 1 false

jimthompson5910 (jim_thompson5910):

B will keep growing and growing. The sum won't converge to a fixed number

OpenStudy (adryin):

Thats what I'm thinking for all the equations

OpenStudy (adryin):

for c d= -0.5 and arithmetics go on forever

jimthompson5910 (jim_thompson5910):

what is the value of r for choice A?

OpenStudy (adryin):

r = \[-\sqrt{2}\]

OpenStudy (adryin):

I think thats convergent but not sure

jimthompson5910 (jim_thompson5910):

correct r value, but it doesn't converge since r = -sqrt(2) = -1.414 approx r = -1.414 makes |r| < 1 false ie, r = -1.414 is more than 1 unit away from 0 on the number line

jimthompson5910 (jim_thompson5910):

A will grow forever just like B does, just at a slower pace

OpenStudy (adryin):

None of these equations converge then?

jimthompson5910 (jim_thompson5910):

what's the r value for E ?

OpenStudy (adryin):

r = 2

jimthompson5910 (jim_thompson5910):

so E diverges

jimthompson5910 (jim_thompson5910):

what's the r value of D ?

OpenStudy (adryin):

d = -12

OpenStudy (adryin):

Wait...

jimthompson5910 (jim_thompson5910):

no it's not arithmetic

OpenStudy (adryin):

I was thinking that

OpenStudy (adryin):

OH.... r = 3/4 so it is convergent

jimthompson5910 (jim_thompson5910):

yep r = 0.75 makes |r| < 1 true since it's between r = -1 and r = 1

OpenStudy (adryin):

Thank you so much!

jimthompson5910 (jim_thompson5910):

no problem

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