Observe the graph:

The graph of the function passes through the origin and it has minimum amplitude at $\"\"$ .

Hence, the graph of the function is cosine function.

The general form of cosine functon is $\"\"$ .

The negative sign indicates that the function flips about $\"\"$ -axis and the midline of the graph is $\"\"$ .

Amplitude of the graph is $\"\"$ .

The graph of the function starts at $\"\"$ and completes one cycle at $\"\"$ .

Period is $\"\"$ .

$\"\"$ .

Substitute $\"\"$ and $\"\"$ in $\"\"$ .

$\"\"$ .

The function of the graph is $\"\"$ .