\(\text{Đạt:A=}\sqrt{4-\sqrt{7}}-\sqrt{4+\sqrt{7}}\text{ dê thấy: A bé hon 0};A^2=4-\sqrt{7}+4+\sqrt{7}-2\sqrt{\left(4-\sqrt{7}\right)\left(4+\sqrt{7}\right)}=8-2\sqrt{16-7}=8-2\sqrt{9}=8-6=2\Rightarrow A=-\sqrt{2}\left(A< 0\right)\Rightarrow\sqrt{4-\sqrt{7}}-\sqrt{4+\sqrt{7}}+\sqrt{8}=-\sqrt{2}+\sqrt{2^2.2}=-\sqrt{2}+2\sqrt{2}=\sqrt{2}\)