căn (27-12 căn 5 ) căn ( 3- căn 5)

$\sqrt{27-12\sqrt{5}}=\sqrt{15-2.\sqrt{15}.\sqrt{12}+12}=\sqrt{(\sqrt{15}-\sqrt{12})^{2}}=\sqrt{15}-\sqrt{12}$

$\sqrt{3-\sqrt{5}}=\sqrt{\frac{6-2\sqrt{5}}{2}}=\sqrt{\frac{5-2.\sqrt{5}.1+1}{2}}=\sqrt{\frac{(\sqrt{5}-1)^{2}}{2}}=\frac{\sqrt{5}-1}{\sqrt{2}}=\frac{\sqrt{10}-\sqrt{2}}{2}$