Question

Tìm đkxđ giải giúp mình câu 19,21,23,24,18,10,13 với

Answer 1

\(19,ĐKXĐ:\dfrac{-2\sqrt{6}+\sqrt{23}}{-x+5}\ge0;x\ne5\\ \Leftrightarrow5-x< 0\left(-2\sqrt{6}+\sqrt{23}< 0\right)\\ \Leftrightarrow x>5\)

\(21,ĐKXĐ:x\ne7;\dfrac{2\sqrt{15}-\sqrt{59}}{x-7}\ge0\\ \Leftrightarrow x-7>0\left(2\sqrt{15}-\sqrt{59}>0\right)\\ \Leftrightarrow x>7\)

\(23,ĐKXĐ:49x^2-24x+4\ge0\Leftrightarrow\left(49x^2-14\cdot\dfrac{12}{7}x+\dfrac{144}{49}\right)+\dfrac{52}{49}\ge0\\ \Leftrightarrow\left(7x-\dfrac{12}{7}\right)^2+\dfrac{52}{49}\ge0\\ \Leftrightarrow x\in R\)