Upgrade to access all content for this subject

Find the formula for the geometric sequence with the first term $a_{1}=-5$ and the fourth term $a_{4}=320$.

$a_{n}=-5\left( 4 \right)^{n-1}$

$a_{n}=-5\left( -4 \right)^{n-1}$

$a_{n}=5\left( -4 \right)^{n-1}$

$a_{n}=5\left( 4 \right)^{n-1}$

none of the above