[tex]a_n = -25 \cdot 2^{n-1},\ \forall \, n \geq 1[/tex]
The general formula for a geometric sequence is:
[tex]a_n = a_1 \cdot r^{n-1},\ \forall \, n \geq 1[/tex]
where [tex]a_1[/tex] is the first term, and [tex]r[/tex] is the ratio.
You can guess the ratio by dividing any term by the previous one. In this case, for example, -50/-25 = 2, and the ratio is 2.
