Find the First Term a_n=4(5)^(n-1)

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

Substitute in the value of $n$ to find the $n$ th term.

$a_{1} = 4 {(5)}^{(1) - 1}$

Subtract $1$ from $1$ .

$a_{1} = 4 \cdot 5^{0}$

Anything raised to $0$ is $1$ .

$a_{1} = 4 \cdot 1$

Multiply $4$ by $1$ .

$a_{1} = 4$