\(x-y=5\Leftrightarrow\left(x-y\right)^2=25\)
\(\Leftrightarrow x^2-2xy+y^2=25\)
\(\Leftrightarrow15-2xy=25\)
\(\Leftrightarrow2xy=-10\)
\(\Leftrightarrow xy=-5\)
Từ đó : \(M=x^3-y^3=\left(x-y\right)\left(x^2+xy+y^2\right)=5\cdot\left(15-5\right)=50\)
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