The value of \(\frac{1}{\sqrt {7 - 4\sqrt {3}}}\) approximately is:

4.1 3.7 4.2 1.2

3.7

\(\frac{1}{\sqrt {7 - 4\sqrt {3}}}\)  →  This is always a square of any term.  \(\frac{1}{\sqrt {(2 - \sqrt {3})^2}}\) = \(\frac{1}{2 - \sqrt {3}}\) × \(\frac{2 + \sqrt {3}}{2 + \sqrt {3}}\)   (rationalisation) \(\frac{2 + \sqrt {3}}{(2)^2 - (\sqrt {3})^2}\) = \(\frac{2 + 1.7}{1}\) = 3.7