\(\sqrt{7+4\sqrt{3}}-\left(4\sqrt{3}-7\right)^2\\ =\sqrt{2^2+2.2.\sqrt{3}+\left(\sqrt{3}\right)^2}-\left|4\sqrt{3}-7\right|\\ =\sqrt{\left(2+\sqrt{3}\right)^2}-\left|4\sqrt{3}-7\right|\\ =\left|2+\sqrt{3}\right|-\left|4\sqrt{3}-7\right|\\ =2+\sqrt{3}-4\sqrt{3}-7\\ =-5-3\sqrt{3}\)