If $u= \sin^{-1} \bigg(\large\frac{x}{y}\bigg)$$+\tan^{-1} \bigg(\large\frac{y}{x}\bigg)$, then the value of $x \large\frac{\partial u}{\partial x}$$+y \large\frac{\partial u}{\partial y}$ is :

Question

$$\begin {array} {1 1} (a)\;0 & \quad (b)\;1 \\ (c)\;2 & \quad (d)\;none\;of\;these \end {array}$$