Step 1 :

The function is $\"\"$ .

The tangent line of the function is horizontal, means that, the slope of the tangent line is zero.

Set slope = $\"image\"$ .

The function is $\"\"$ .

Differentiate the function with respect to $\"\"$ .

$\"\"$

Apply quotient rule of derivatives : $\"\"$ .

$\"\"$

Apply power rule of derivatives : $\"image\"$ .

$\"\"$

Step 2 :

At $\"\"$ , $\"\"$ .

At the points $\"\"$ . the graph of the function has a horizontal tangent line.

Solution :

At the points $\"\"$ . the graph of the function $\"\"$ has a horizontal tangent line.