(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 .