(a) The function , .

Derivative of a function  is  at  defined as .

Substitute  in above formula.

.

(b) 

Substitute  in above function.

The function is undefined when the denominator is zero.

So  does not exist.

(c) .

Slope of the tangent to the curve  at the point  is .

Slope of the tangent to the curve  at  is .

This means that  has a vertical tangent line at .

(a) .

(b)  does not exist.

(c) The function has vertical tangent line at .