$\"\"$

The arithmetic sequence is $\"\"$ .

Find $\"\"$ th term of the arithmetic sequence :

Here, $\"\"$ and $\"\"$ .

The formula for $\"\"$ th term of the arithmetic sequence : $\"\"$ .

$\"\"$ (Subtitute $\"\"$ and $\"\"$ )

$\"\"$ (Simplify)

Thus, the related function is $\"\"$ .

$\"\"$

Graph :

Draw a coordinate plane.

Graph the function $\"\"$ to determine the function is proportional or nonproportional.

$\"\"$

Observe the graph :

The graph of the line does not passes through the origin $\"\"$ .

Therefore, the function is nonproportional.

Therefore, the function does not describe a direct variation.

$\"\"$

The function is $\"\"$ ; It is nonproportional ; The function does not describe a direct variation.