(a)

The function is  .

Differentiate on each side with respect to .

Quotient rule of derivatives: .

If is a function , which is differentiable and  is an independent  variable.

Then the differential in terms of  is defined as .

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(b)

The function is .

Differentiate on each side with respect to .

Product rule of derivatives: .

To get differential , multiply both sides with .

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(a) .

(b) .