Find a Formula for the Nth Term of the Sequence $1 , - \frac { 1 } { 4 } , \frac { 1 } { 9 } , - \frac { 1 } { 16 } , \frac { 1 } { 25 }$

Multiple Choice

Find a formula for the nth term of the sequence.
- $1 , - \frac { 1 } { 4 } , \frac { 1 } { 9 } , - \frac { 1 } { 16 } , \frac { 1 } { 25 }$ (reciprocals of squares with alternating signs)

A) $a _ { n } = \frac { ( - 1 ) ^ { n ^ { 2 } } } { n ^ { 2 } }$
B) $a _ { n } = \frac { ( - 1 ) ^ { n } } { n ^ { 2 } }$
C) $a _ { n } = \frac { ( - 1 ) ^ { 2 n + 1 } } { n ^ { 2 } }$
D) $a _ { n } = \frac { ( - 1 ) ^ { n + 1 } } { n ^ { 2 } }$