Rút gọn: (√28 - √12 - √7) . (√7 + 2√21)

1, Rút gọn.
$a,$ $(\sqrt{28}-\sqrt{12}-\sqrt{7}).\sqrt{7}+2\sqrt{21)}$
$b, \frac{5+\sqrt{5}}{5-\sqrt{5}}+\frac{5-\sqrt{5}}{5+\sqrt{5}}$
$c, \frac{1}{7+4\sqrt{3}}+\frac{1}{7-4\sqrt{3}}$
$d, (2+\sqrt{5}+\sqrt{3}).(2+\sqrt{5}-\sqrt{3})$
$e, (\frac{1}{\sqrt{5}-\sqrt{2}}-\frac{1}{\sqrt{5}+\sqrt{2}}+1).\frac{1}{{(\sqrt{2}+1)}^2}$