Let $z = \sin u = \frac{x^2 y}{x + y}$.
Testing homogeneity of $z(x, y)$:
$$z(tx, ty) = \frac{(tx)^2 (ty)}{tx + ty} = \frac{t^3 x^2 y}{t(x + y)} = t^2 z(x, y)$$
Thus, $z = \sin u$ is a homogeneous function of degree $n = 2$.
By Euler's Theorem for homogeneous functions:
$$x\frac{\partial z}{\partial x} + y\frac{\partial z}{\partial y} = n z = 2\sin u$$
Since $z = \sin u$, we have $\frac{\partial z}{\partial x} = \cos u \frac{\partial u}{\partial x}$ and $\frac{\partial z}{\partial y} = \cos u \frac{\partial u}{\partial y}$:
$$x \cos u \frac{\partial u}{\partial x} + y \cos u \frac{\partial u}{\partial y} = 2\sin u$$
$$x\frac{\partial u}{\partial x} + y\frac{\partial u}{\partial y} = \frac{2\sin u}{\cos u} = 2\tan u$$
Hence, Option 1 is correct.
मान लीजिए $z = \sin u = \frac{x^2 y}{x + y}$:
$z$ घात $n = 3 - 1 = 2$ का एक समघात फलन (homogeneous function) है।
ऑयलर के समघात फलन प्रमेय से:
$$x\frac{\partial z}{\partial x} + y\frac{\partial z}{\partial y} = 2 z = 2\sin u$$
$$\cos u \left(x\frac{\partial u}{\partial x} + y\frac{\partial u}{\partial y}\right) = 2\sin u$$
$$x\frac{\partial u}{\partial x} + y\frac{\partial u}{\partial y} = 2\frac{\sin u}{\cos u} = 2\tan u$$
अतः विकल्प 1 सही उत्तर है।