Question:

If \( x\sin(a+y) + \sin a \cos(a+y)=0 \), then \( \frac{dy}{dx} \) is equal to

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Use given equation again after differentiation to simplify.
Updated On: Apr 23, 2026
  • $\frac{\sin^2(a+y)}{\sin a}$
  • $\frac{\cos^2(a+y)}{\cos a}$
  • $\frac{\sin^2(a+y)}{\cos a}$
  • $\frac{\cos^2(a+y)}{\sin a}$
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The Correct Option is A

Solution and Explanation

Concept: Implicit differentiation.

Step 1:
Differentiate both sides.
\[ \frac{d}{dx}[x\sin(a+y)] + \frac{d}{dx}[\sin a \cos(a+y)] = 0 \]

Step 2:
Apply product rule.
\[ \sin(a+y) + x\cos(a+y)\frac{dy}{dx} - \sin a \sin(a+y)\frac{dy}{dx} = 0 \]

Step 3:
Group $\frac{dy}{dx}$.
\[ \sin(a+y) + \frac{dy}{dx}[x\cos(a+y) - \sin a \sin(a+y)] = 0 \]

Step 4:
Solve for $\frac{dy}{dx}$.
\[ \frac{dy}{dx} = \frac{-\sin(a+y)}{x\cos(a+y) - \sin a \sin(a+y)} \]

Step 5:
Use original equation.
From given: \[ x\sin(a+y) = -\sin a \cos(a+y) \] Substitute and simplify: \[ \frac{dy}{dx} = \frac{\sin^2(a+y)}{\sin a} \] Conclusion:
Answer = Option (A)
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