The equation is $\"\"$ .

Graph the curve $\"\"$ .

$\"\"$

The equation is $\"\"$ .

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

Slope of the tangent is derivative of the curve.

$\"\"$ .

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

$\"\"$

Equate the above expression to zero.

$\"\"$

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

Hence there are three horizontal tangent lines.

$\"\"$ - coordinates of horizontal tangent lines are $\"\"$ , $\"\"$ and $\"\"$ .

(a)

Graph the curve $\"\"$ is

$\"\"$

(b)

There are three horizontal tangent lines.

$\"\"$ - coordinates of horizontal tangent lines are $\"\"$ , $\"\"$ and $\"\"$ .