$\"\"$

The vertical translation form of the cosine function with left phase shift is $\"\"$ .

Where amplitude $\"\"$ and period $\"\"$ .

Here,

Amplitude $\"\"$ ,

Period $\"\"$

$\"\"$ .

Phase shift $\"\"$ .

$\"\"$

Since vertical translation $\"\"$ down wards, $\"\"$ .

Substitute the corresponding values in $\"\"$ .

$\"\"$

The cosine function is $\"\"$ .