$\"\"$

The given values are $\"\"$ .

Where $\"\"$ is the first term and $\"\"$ is the nth term.

The sum of an arithmetic series $\"\"$ .

$\"\"$

$\"\"$ (Substitute $\"\"$ )

$\"\"$ (Add: $\"\"$ )

$\"\"$ (Multiply: $\"\"$ )

$\"\"$ (Divide: $\"\"$ $\"\"$ ) $\"\"$

The value of $\"\"$ .