cho x,y,z >0 thoả mãn \(\left(1+\dfrac{1}{x}\right)\left(1+\dfrac{1}{y}\right)\left(1+\dfrac{1}{z}\right)=8\)

tìm Max: \(P=\dfrac{x^2+y^2+z^2+14xyz}{4\left(x+y+z\right)+15xyz}\)

giải hệ pt

\(\left\{{}\begin{matrix}x^3+3xy^2=-49\\x^2-8xy+y^2=8y-17x\end{matrix}\right.\)