The function is .

Differentiate on each side with respect to .

Quotient rule of derivatives: .

\ \ Pythagorean identity: .

.

(b) .

Quotient identity:  and .

Substitute above values in the function.

Differentiate on each side with respect to .

Derivative of the sine function: .

Derivative of the cosine function: .

. \ \

(c)

Consider the result of (a),.

.

Quotient identity: and .

.

Above result is same as the result of (b).

Therefore results of (a) and (b) are same.

(a) .

(b) .