(a)

The function is .

Apply derivative on each side with respect to .

The chain rule of derivative : .

.

.

Use the power rule : .

.

If  is a function, which is differentiable and   is an independent variable, then the differential  in terms of  is defined as .

.

(b)

The function is .

Apply derivative on each side with respect to .

.

Quotient rule of derivatives: .

.

Differential of the function is .

(a) .

(b) .