Use the Geometric Series Formula to Find the Sum Of 1

Essay

Use the geometric series formula to find the sum of $1 - \frac { 1 } { r } + \frac { 1 } { r ^ { 2 } } - \frac { 1 } { r ^ { 3 } } + \frac { 1 } { r ^ { 4 } } + \cdots \pm \frac { 1 } { r ^ { n - 1 } }$ ,where the $\pm$ denotes + if n is odd and – if n is even (to fit the pattern of the earlier terms).