\(A=\dfrac{\sqrt{10}-\sqrt{15}}{\sqrt{8}-\sqrt{12}}=\dfrac{\sqrt{2.5}-\sqrt{3.5}}{\sqrt{4.2}-\sqrt{4.3}}=\dfrac{\sqrt{5}\left(\sqrt{2}-\sqrt{3}\right)}{\sqrt{4}\left(\sqrt{2}-\sqrt{3}\right)}=\dfrac{\sqrt{5}}{\sqrt{4}}=\dfrac{\sqrt{5}}{2}\)
\(B=\dfrac{\sqrt{2.3}-\sqrt{5.3}}{\sqrt{7.5}-\sqrt{7.2}}=\dfrac{\sqrt{3}\left(\sqrt{2}-\sqrt{5}\right)}{-\sqrt{7}\left(\sqrt{2}-\sqrt{5}\right)}=-\dfrac{\sqrt{3}}{\sqrt{7}}=-\dfrac{\sqrt{21}}{7}\)
\(C=\dfrac{5+\sqrt{5}}{\sqrt{10}+\sqrt{2}}=\dfrac{\sqrt{5}\left(\sqrt{5}+1\right)}{\sqrt{2}\left(\sqrt{5}+1\right)}=\dfrac{\sqrt{5}}{\sqrt{2}}=\dfrac{\sqrt{10}}{2}\)
\(D=\dfrac{\sqrt{5.3}-\sqrt{5}}{\sqrt{3}-1}+\dfrac{\sqrt{5^2}-2\sqrt{5}}{2\sqrt{5}-2.2}=\dfrac{\sqrt{5}\left(\sqrt{3}-1\right)}{\sqrt{3}-1}+\dfrac{\sqrt{5}\left(\sqrt{5}-2\right)}{2\left(\sqrt{5}-2\right)}\)
\(=\sqrt{5}+\dfrac{\sqrt{5}}{2}=\dfrac{3\sqrt{5}}{2}\)
