(a) Find $\frac{dy}{dx}$, if $(\cos x)^y = (\cos y)^x$. OR (b) If $\sqrt{1-x^2} + \sqrt{1-y^2} = a(x-y)$, prove that $\frac{dy}{dx} = \sqrt{\frac{1-y^2}{1-x^2}}$.

Year	Paper Code	Set	Position
CBSE 2024	Series Other	Set 1	Question 26
CBSE 2024	Series Other	Set 1	Question 28
CBSE 2024	Series Other	Set 1	Question 29

• Step 1: Stating the fundamental formula / law statement (+1 Mark)
• Step 2: Intermediate mathematical substitution or proof steps (+1 Mark)
• Step 3: Correct final value or conclusion with mandatory SI units (+1 Mark)