Tìm \(x;y\in Z\)

\(x^3-y^3=6xy+3\)

Chứng Minh :

\(cos\left(2\alpha\right)=Cos^2\alpha-Sin^2\alpha\)

cho \(\dfrac{1}{\text{x}}+\dfrac{1}{y}+\dfrac{1}{z}=3\) tìm GTLN của :

\(\dfrac{1}{\sqrt{2\text{x}^2+y^2+3}}+\dfrac{1}{\sqrt{2y^2+z^2+3}}+\dfrac{1}{\sqrt{2z^2+\text{x}^2+3}}\)