а)

[tex] \sqrt{ {6.8}^{2} - {3.2}^{2} } = \sqrt{(6.8 - 3.2)(6.8 + 3.2)} = \\ \sqrt{3.6\times 10} = \sqrt{36} = \sqrt{6 {}^{2} } = 6[/tex]

б)

[tex] \sqrt{ \frac{98}{228 {}^{2} - {164}^{2} } } = \sqrt{ \frac{98}{(228 - 164)(228 + 164)} } = \\ \sqrt{ \frac{98}{64 \times 392} } = \sqrt{ \frac{1}{ {8}^{2} \times {2}^{2} } } = \frac{1}{8 \times 2} = \frac{1}{16} [/tex]