$a)\left|3\right|=3$

$b)\left|-7\right|=7$

$c)\left|\frac{1}{7}\right|=\frac{1}{7}$

$d)\left|5-\sqrt{5}\right|\stackrel{{}^{\left(5-\sqrt{5}\approx 5-2,23>0\right)}}{=}5-\sqrt{5}$

$e)\left|\frac{1}{5}-\frac{1}{\sqrt{5}}\right|\stackrel{{}^{\left(\frac{1}{5}-\frac{1}{\sqrt{5}}\approx \frac{1}{5}-\frac{1}{2,23}<0\right)}}{=}-\left(\frac{1}{5}-\frac{1}{\sqrt{5}}\right)=\frac{1}{\sqrt{5}}-\frac{1}{5}$

$f)\left|2^3-{\pi }^2\right|\stackrel{{}^{\left(2^3-{\pi }^2=8-3,14\cdot 3,14<0\right)}}{=}-\left(2^3-{\pi }^2\right)={\pi }^2-2^3$