2.5:
\(2\sqrt{3}\left(\sqrt{3}-2\right)+4\sqrt{3}=2\sqrt{3}.\sqrt{3}-2\sqrt{3}.2+4\sqrt{3}=6-4\sqrt{3}+4\sqrt{3}=6\)
2.6:
\(-8\sqrt{3}-4\sqrt{3}\left(\dfrac{1}{2}\sqrt{3}-2\right)=-8\sqrt{3}-4\sqrt{3}.\dfrac{1}{2}\sqrt{3}+8\sqrt{3}=-8\sqrt{3}-6+8\sqrt{3}=-6\)