\(a.\dfrac{1\left(7-4\sqrt{3}\right)}{\left(7+4\sqrt{3}\right)\left(7-4\sqrt{3}\right)}+\dfrac{1\left(7+4\sqrt{3}\right)}{\left(7+4\sqrt{3}\right)\left(7-4\sqrt{3}\right)}=7-4\sqrt{3}+7+4\sqrt{3}=14\)
\(a,=\dfrac{7-4\sqrt{3}+7+4\sqrt{3}}{\left(7+4\sqrt{3}\right)\left(7-4\sqrt{3}\right)}=\dfrac{14}{49-48}=14\\ b,=\dfrac{15\left(\sqrt{6}-1\right)}{5}+\dfrac{4\left(\sqrt{6}-2\right)}{2}-\dfrac{12\left(3+\sqrt{6}\right)}{3}-\sqrt{6}\\ =3\sqrt{6}-3+2\sqrt{6}-4-12-4\sqrt{6}-\sqrt{6}\\ =-19\\ c,=\dfrac{\sqrt{2}-1-2+\left(\sqrt{2}+1\right)^2}{\sqrt{2}\left(\sqrt{2}+1\right)}=\dfrac{\sqrt{2}-3+3-2\sqrt{2}}{\sqrt{2}\left(\sqrt{2}+1\right)}\\ =\dfrac{-\sqrt{2}}{\sqrt{2}\left(\sqrt{2}+1\right)}=\dfrac{-1}{\sqrt{2}+1}\)
