$\"\"$

The trigonometric identity is $\"open$ .

Start the left side $\"open$

Apply pythagorean identity: $\"Syntax$ .

$\"open$

$\"open$ $\"\"$

Apply double-angle formula: $\"italic$ .

$\"open$

$\"equal$

Apply double-angle formula: $\"italic$ .

$\"equal$

Apply double-angle formula: $\"italic$ .

$\"equal$

$\"\"$

The trigonometric identity is $\"open$ is "true".