1: Thay x=3 và y=-1 vào hệ, ta được:
\(\left\{{}\begin{matrix}a\cdot3+b\cdot\left(-1\right)=3\\b\cdot3-a\cdot\left(-1\right)=11\end{matrix}\right.\)
=>\(\left\{{}\begin{matrix}3a-b=3\\a+3b=11\end{matrix}\right.\)
=>\(\left\{{}\begin{matrix}9a-3b=9\\a+3b=11\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}9a-3b+a+3b=20\\a+3b=11\end{matrix}\right.\)
=>\(\left\{{}\begin{matrix}10a=20\\3b=11-a\end{matrix}\right.\)
=>\(\left\{{}\begin{matrix}a=2\\3b=11-2=9\end{matrix}\right.\)
=>\(\left\{{}\begin{matrix}a=2\\b=3\end{matrix}\right.\)
2: ĐKXĐ: \(x\in R\)
\(\sqrt{x^2-2x+4}=2\)
=>\(x^2-2x+4=2^2=4\)
=>\(x^2-2x=0\)
=>x(x-2)=0
=>\(\left[{}\begin{matrix}x=0\\x=2\end{matrix}\right.\)
