\(x^2=\left(\sqrt{21+6\sqrt{6}}-\sqrt{21-6\sqrt{6}}\right)^2\)
\(x^2=21+6\sqrt{6}+21-6\sqrt{6}-2\sqrt{441-216}\)
\(x^2=42-2\sqrt{225}\)
\(x^2=42-30=12\)
\(x=2\sqrt{3}\)
nếu có sai bn thông cảm nha
cách khác nhé:
\(\sqrt{21+6\sqrt{6}}-\sqrt{21-6\sqrt{6}}\)
\(=\sqrt{21+2.3\sqrt{2}.\sqrt{3}}-\sqrt{21-2.3\sqrt{2}.\sqrt{3}}\)
\(=\sqrt{18+2.\sqrt{18}.\sqrt{3}+3}-\sqrt{18-2.\sqrt{18}.\sqrt{3}+3}\)
\(=\sqrt{\left(\sqrt{18}+\sqrt{3}\right)^2}-\sqrt{\left(\sqrt{18}-\sqrt{3}\right)^2}\)
\(=\left(\sqrt{18}+\sqrt{3}\right)-\left(\sqrt{18}-\sqrt{3}\right)\)
\(=2\sqrt{3}\)
p/s: mk đã phân tích kĩ ra cho bn rồi đó