`đkxđ`
`A=`$\sqrt{(x-1)(x-3)}$
`=>` \(\left[ \begin{array}{l}\begin{cases} x-3\geq0\\x-1 \geq0\end{cases}\\\begin{cases} x-3\leq0 \\x-1\leq0\end{cases}\end{array} \right.\)`<=>`\(\left[ \begin{array}{l}\begin{cases} x\geq3\\x\geq1\end{cases}\\\begin{cases} x\leq3\\x\leq1\end{cases}\end{array} \right.\) `<=>`\(\left[ \begin{array}{l}x \geq3\\x\leq 1\end{array} \right.\)
vậy `x>=3 hoặc x<=1` thì `A xđ`
`B=`$\sqrt[]{x^{2}-4}$
`B xđ <=>x^2-4>=0`
`<=> x^2>=4`
`<=>`\(\left[ \begin{array}{l}-x\geq2\\x\geq2\end{array} \right.\)`<=>` \(\left[ \begin{array}{l}x\leq-2\\x\geq2\end{array} \right.\)
vậy `x>=2;x<=-2` thì `B` xđ
