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Mathematics 8 Online
OpenStudy (anonymous):

Please help, the sooner the better :)

OpenStudy (jdoe0001):

57

OpenStudy (anonymous):

What is the sum of the geometric series?

OpenStudy (anonymous):

-.- very funny

OpenStudy (anonymous):

LOL!

OpenStudy (jdoe0001):

\(\large { \textit{sum of geometric sequence}=S{\color{brown}{ n}}=a_1\left( \cfrac{1-r^{\color{brown}{ n}}}{1-r} \right)\qquad\\ \quad \\ \Sigma_{n=1}^{10}\quad 6(2)^{\color{brown}{ n}} \\ \quad \\ a_1\to \textit{first term of sequence} }\)

OpenStudy (anonymous):

oh dear, many numbers and letters... ok...

OpenStudy (jdoe0001):

so in this case since n = 10 then \(\bf S_{\color{brown}{ 10}}=a_1\left( \cfrac{1-r^{\color{brown}{ 10}}}{1-r} \right)\)

OpenStudy (anonymous):

oh ok that makes a bit of sense

OpenStudy (anonymous):

so am I trying to figure out what S is?

OpenStudy (jdoe0001):

ohh S is jus the notation for "S"um

OpenStudy (anonymous):

I'm already confused :(

OpenStudy (jdoe0001):

another way of saying if we have "n" terms, beginning at \(a_1\) the "S"um of it will be this

OpenStudy (anonymous):

oh ok, then why does it have base 10?

OpenStudy (jdoe0001):

it is not a base yes, it looks like that because is a subscript of the letter is just a way to say "a sum that goes up to "n"th number"

OpenStudy (anonymous):

ah ok

OpenStudy (jdoe0001):

hmmm actually we haven't plugged in "r" one sec

OpenStudy (anonymous):

ok

OpenStudy (anonymous):

I have to go, please continue to explain and I will read it when I come back

OpenStudy (jdoe0001):

\(\large { \bf \textit{sum of geometric sequence}=S_{\color{brown}{ n}}=a_1\left( \cfrac{1-{\color{blue}{ r}}^{\color{brown}{ n}}}{1-{\color{blue}{ r}}} \right) \\ \quad \\ \qquad a_1\to \textit{first term of the sequence} \\ \quad \\ \Sigma_{{\color{brown}{ n}}=1}^{10}\quad 6({\color{blue}{ 2}})^{\color{brown}{ n}}\implies S_{\color{brown}{ 10}}=a_1\left( \cfrac{1-{\color{blue}{ 2}}^{\color{brown}{ 10}}}{1-{\color{blue}{ 2}}} \right) }\)

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