1,
\(x^2+y^2+y^2=14\)
\(\Rightarrow\left(x+y+z\right)^2-2xy-2yz-2zx=14\)
\(\Rightarrow-2\left(xy+yz+zx\right)=14\)
\(\Rightarrow xy+yz+zx=-7\)
\(\Rightarrow\left(xy+yz+zx\right)^2=49\)
\(\Leftrightarrow x^2y^2+y^2z^2+z^2x^2+2x^2yz+2xy^2z+2xyz^2=49\)
\(\Leftrightarrow x^2y^2+y^2z^2+z^2x^2+2xyz\left(x+y+z\right)=49\)
\(\Leftrightarrow x^2y^2+y^2z^2+z^2x^2=49\)
Ta có: \(x^4+y^4+z^4\)
\(=\left(x^2+y^2+z^2\right)^2-2x^2y^2-2y^2z^2-2z^2x^2\)
\(=14^2-2\left(x^2y^2+y^2z^2+z^2x^2\right)\)
\(=14^2-2.49\)
\(=196-98\)
\(=98\)