Solution
xy(x+y)=1
x+y = 1/xy
apply cube on both sides,
$$(x+y)^{3}$$ = $$\frac{1}{x^{3}y^{3}}$$
$$x^{3}+y^{3}+3xy(x+y)$$ = $$\frac{1}{x^{3}y^{3}}$$
$$x^{3}+y^{3}+3(1)$$ = $$\frac{1}{x^{3}y^{3}}$$
3 = $$\frac{1}{x^{3}y^{3}}$$ - $$x^{3}-y^{3}$$
so the answer is option A.
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