Question

Rút gọn: Giải từng bước giúp em với please

Answer 1

13.

\(\left(\sqrt{7}-\sqrt{3}\right)\sqrt{10+2\sqrt{21}}=\left(\sqrt{7}-\sqrt{3}\right)\sqrt{7+2.\sqrt{7}.\sqrt{3}+3}\)

\(=\left(\sqrt{7}-\sqrt{3}\right)\sqrt{\left(\sqrt{7}+\sqrt{3}\right)^2}=\left(\sqrt{7}-\sqrt{3}\right)\left|\sqrt{7}+\sqrt{3}\right|=\left(\sqrt{7}-\sqrt{3}\right)\left(\sqrt{7}+\sqrt{3}\right)\)

\(=7-3=4\)

15.

\(\left(\sqrt{6}-\sqrt{14}\right)\sqrt{5+\sqrt{21}}=\left(\sqrt{3}-\sqrt{7}\right).\sqrt{2}.\sqrt{5+\sqrt{21}}\)

\(=-\left(\sqrt{7}-\sqrt{3}\right)\sqrt{10+2\sqrt{21}}=...\) lặp lại câu trên \(=-4\)