Đề \(\leftrightarrow \frac{(1-\sqrt{2})(1-\sqrt{2})-(1+\sqrt{2})(1+\sqrt{2})}{(1+\sqrt{2})(1-\sqrt{2}).6\sqrt{2}}=\frac{(1-\sqrt{2})^{2}-(1+\sqrt{2})^{2}}{(1-2)6\sqrt{2}}=\frac{1-2\sqrt{2}+2-(1+2\sqrt{2}+2)}{-6\sqrt{2}}=\frac{-4\sqrt{2}}{-6\sqrt{2}}=\frac{2}{3}\)
