\(\left(2+\sqrt{3}\right).\sqrt{7-4\sqrt{3}}=\left(2+\sqrt{3}\right).\sqrt{3-4\sqrt{3}+2}=\left(2+\sqrt{3}\right).\sqrt{\left(\sqrt{3}-2\right)^2}=\left(2+\sqrt{3}\right).\left|\sqrt{3}-2\right|=\left(2+\sqrt{3}\right).\left(2-\sqrt{3}\right)=4-3=1\)