No clue on this on… - QuestionCove
OpenStudy (anonymous):

No clue on this one: "Find the sum, if it exists: 125-25+5-1+1/5..."

6 years ago
OpenStudy (anonymous):

there are no notations on when the sequence terminates, just the ... at the end. I can see the sequence is being divided by -5, but...?

6 years ago
OpenStudy (anonymous):

$a= 125$ $r =\frac{-1}{5}$

6 years ago
OpenStudy (anonymous):

$S = \frac{125}{1 + \frac{1}{5}}$

6 years ago
OpenStudy (anonymous):

$S = \frac{625}{6}$

6 years ago
OpenStudy (anonymous):

i'm confused - the ... means the sequence doesn't terminate though, or?

6 years ago
OpenStudy (anonymous):

$S = \frac{a(1 -r^n)}{(1-r)}$

6 years ago
OpenStudy (anonymous):

when r<1 and n-> infinity r^n ~0 Hence the formula becomes $S = \frac{a}{1-r}$

6 years ago
OpenStudy (anonymous):

$\S_{\infty}=a1/(1-r)$ is the formula i have, so 125/1.2 = 104.167?

6 years ago
OpenStudy (anonymous):

r=-1/5 so denominator becomes 1 +1/5 =6/5 = 1.2 yeah you are correct

6 years ago