[tex] 9( \frac{1}{3\sqrt{2}}-\frac{1}{2\sqrt{2}} +\frac{1}{6\sqrt{2}} -\frac{1}{12\sqrt{2}} )=9(\frac{\sqrt{2}}{6}-\frac{\sqrt{2}}{4} +\frac{\sqrt{2}}{12}-\frac{\sqrt{2}}{24} )=\\ \\ =9\sqrt{2} (\frac{1}{6} -\frac{1}{4} +\frac{1}{12} -\frac{1}{24} )=9\sqrt{2}*\frac{4-6+2-1}{24} =9\sqrt{2}*\frac{-1}{24} =-\frac{9\sqrt{2}}{24} =-\frac{3\sqrt{2}}{8} [/tex]
