(a)  .

Tangent line or linear approximation formula:

.

Here consider , and .

.

Differentiate on each side with respect to .

.

.

Substitute corresponding values in the linear approximation formula.

(b) .

Tangent line or linear approximation formula:

.

Here consider , and .

.

Differentiate on each side with respect to .

.

Substitute corresponding values in the linear approximation formula.

.

(a)

(b) .