Write the Expression for the General (Or Nth)termrm $\mathbf { a } _ { \mathbf { n } } ,$

Multiple Choice

Write the expression for the general (or nth) termrm, $\mathbf { a } _ { \mathbf { n } } ,$ , of the geometric sequence.
-5, 10, 20, 40, 80,. . .

A) $a _ { n } = 5 ( 2 ) ^ { n - 1 }$
B) $a _ { n } = 5 ( 2 n )$
C) $a _ { n } = a _ { 1 } + 2 ^ { n }$
D) $a _ { n } = 5 ( 2 ) ^ { n }$