Nhầm nhầm @@
\(\left\{{}\begin{matrix}x+y=5\\y+z=6\\z+t=7\end{matrix}\right.\) \(\Leftrightarrow x+y+z+t=12\)
\(\Leftrightarrow x+2y+z=11\)
\(\Leftrightarrow\left(x+y+z+t\right)-\left(x+y+y+z\right)=1\)
\(\Leftrightarrow x+y+z+t-x-y-y-z=1\)
\(\Leftrightarrow t-y=1\)
\(\Leftrightarrow y+2z+t=13\)
\(\Leftrightarrow\left(y+z+z+t\right)-\left(x+y+z+t\right)=1\)
\(\Leftrightarrow y+z+z+t-x-y-z-t=1\)
\(\Leftrightarrow z-t=1\)
Ta có:
\(\left\{{}\begin{matrix}z+t=7\\z-t=1\end{matrix}\right.\) \(\Leftrightarrow\left\{{}\begin{matrix}z+t+z-t=8\Rightarrow2z=8\Rightarrow z=4\\t=4-1=3\end{matrix}\right.\)
\(\Rightarrow\left\{{}\begin{matrix}y=6-4=2\\x=5-2=3\end{matrix}\right.\)
Vậy...
\(\left\{{}\begin{matrix}x+y=5\\y+z=6\\z+t=7\end{matrix}\right.\)
\(\Rightarrow\left(x+y\right)-\left(y+z\right)+\left(z+t\right)=5-6+7\)
\(\Rightarrow x+y-y-z+z+t=6\)
\(\Rightarrow x+t=6\)
\(\Rightarrow\left\{{}\begin{matrix}x+y=5\\y+z=6\\z+t=7\\x+t=6\end{matrix}\right.\)
\(\Rightarrow x+y+y+z+z+t+t+x=5+6+7+6\)
\(\Rightarrow2\left(x+y+z+t\right)=18\)
\(\Rightarrow x+y+z+t=9\)
Thay zô tính
