Question

If $u=cos^{-1}\frac{x+y}{\sqrt{x}+\sqrt{y}}$, then the value of $x\frac{\partial u}{\partial x}+y\frac{\partial u}{\partial y}$ is

• A. $\frac{1}{2}\cot u$
• B. $-\frac{1}{2}\cot u$
• C. $-\frac{1}{2}\tan u$
• D. $\frac{1}{2}\tan u$

Answer 1

Answer: (B)

$-\frac{1}{2}\cot u$

Answer 2

The correct answer is(B):