B3. Simplify the expression $\frac{\left(1-\left(\frac{x}{y}\right)^{2}\right) \cdot y^{2} \cdot(x-y)^{-1}}{(\sqrt{x}-\sqrt{y})^{2}+\sqrt{4 x y}}$, given that $x, y>0$ and $x \neq y$.
B3. Let's correct the multiplication and consider the negative exponent $\mathrm{v}$ in the numerator $\left(1-\left(\frac{x}{y}\right)^{2} \cdot y^{2} \cdot(x-y)^{-1}=\right.$ $\left(y^{2}-x^{2}\right) \cdot \frac{1}{x-y}$. Square and partially root in the denominator $(\sqrt{x}-\sqrt{y})^{2}+\sqrt{4 x y}=x-$ $2 \sqrt{x y}+y+2 \sqrt{x y}$. Factor the numerator and simplify the denominator $\frac{(y-x)(y+x) \frac{1}{x-y}}{x+y}$. Simplify and get $(y-x) \frac{1}{x-y}=\frac{y-x}{x-y}$, simplify again and get -1.

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Denominator simplification $x-2 \sqrt{x y}+y+2 \sqrt{x y}=x+y \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots$

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