Find the Third Term a_n=21-2n^2

$a_{n} = 21 - 2 n^{2}$

Step 1

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

$a_{3} = 21 - 2 {(3)}^{2}$

Step 2

Simplify each term.

Raise $3$ to the power of $2$ .

$a_{3} = 21 - 2 \cdot 9$

Multiply $- 2$ by $9$ .

$a_{3} = 21 - 18$

Step 3

Subtract $18$ from $21$ .

$a_{3} = 3$