$\"\"$

The function is $\"y=\\frac{\\cos$ .

Differentiate on each side with respect to $\"x\"$ .

$\"\\small$ .

Quotient rule of derivatives: $\"\\left$ .

$\"\\\\y\'=\\frac{(2+\\sin$

$\"\\\\y\'=\\frac{-2\\sin$

Pythagorean identity: $\"\\cos^2x+\\sin^2x=1\"$ .

$\"\\\\y\'=\\frac{-2\\sin$

Slope of the tangent is derivative of the function.

$\"\\\\m=y\'=\\frac{-2\\sin$ .

The function has horizontal tangent when slope of the tangent is zero.

$\"\\\\y\'=\\frac{-2\\sin$

$\"\\sin$

General solution of $\"\\sin$ is $\"x=n\\pi$ .

$\"x=n\\pi$ .

$\"\"$

$\"x=n\\pi$ .