Question

MEDAL please help me. i dont understand.
"Find the sum, if it converges. (1/3)-(1/9)+(1/27)-..."

Answer 1

its a geometric series

r = -1/3

Answer 2

\[\text{\sum} = \frac{a_1}{1-r}\]

Answer 3

\[\frac{ 1 }{ 3 }-\frac{ 1 }{ 9}+\frac{ 1 }{ 27}\]
common denominator

Answer 4

\[\frac{ 1*9 }{ 3*9 }-\frac{ 1*3 }{ ?9*3 }+\frac{ 1 }{ 27}=\frac{ 9-3+1 }{ 27 }=\]

Answer 5

http://www.wolframalpha.com/input/?i=%5Csum_%7Bi%3D1%7D%5E%7B%5Cinfty%7D%5Cfrac%7B1%7D%7B3%5Ei%7D%28-1%29%5E%7Bi%2B1%7D