\(x+y=3\Rightarrow\left(x+y\right)^2=9\Rightarrow x^2+y^2+2xy=9\)
\(\Rightarrow5+2xy=9\Rightarrow xy=2\)
\(\Rightarrow\left(x-y\right)^2=x^2+y^2-2xy=5-2.2=1\)
\(\Rightarrow x-y=\pm1\)
\(A=\left(x-y\right)\left(x^2+y^2+xy\right)=\pm1.\left(5+2\right)=\pm7\)
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