B
bananamiss
giải hệ
[TEX]\left{\begin{3x-y-5z-2yz=0}\\{x-5y-z-2z^2=0}\\{x+9y-3z+2xz=0}[/TEX]
[TEX]\Leftrightarrow \left{\begin{3x-y-5z-2yz=0 \ (1)}\\{2x-10y-2z-4z^2=0 \ (2)}\\{x+9y-3z+2xz=0\ (3)}[/TEX]
[TEX](1)-(2)-(3) \Leftrightarrow 4z^2-2yz-2xz=0 \Leftrightarrow \left[ z=0 \\ x+y=2z [/TEX]
thế vào hệ ban đầu ~~~> ok