a/ $\sqrt{8-2\sqrt 7}\\=\sqrt{7-2\sqrt 7+1}\\=\sqrt{(\sqrt 7)^2-2.\sqrt 7.1+1^2}\\=\sqrt{(\sqrt 7-1)^2}\\=|\sqrt 7-1|\\=\sqrt 7-1(vì\,\,\sqrt 7-1>0)$
Vậy $\sqrt{8-2\sqrt 7}=\sqrt 7-1$
b/ $\sqrt{7+4\sqrt 3}\\=\sqrt{4+4\sqrt 3+3}\\=\sqrt{2^2+2.2.\sqrt 3+(\sqrt 3)^2}\\=\sqrt{(2+\sqrt 3)^2}\\=|2+\sqrt 3|\\=2+\sqrt 3(vì\,\,2+\sqrt 3>0)$
Vậy $\sqrt{7+4\sqrt 3}=2+\sqrt 3$
c/ $\sqrt{7-2\sqrt 6}\\=\sqrt{6-2\sqrt 6+1}\\=\sqrt{(\sqrt 6)^2-2.\sqrt 6.1+1^2}\\=\sqrt{(\sqrt 6-1)^2}\\=|\sqrt 6-1|\\=\sqrt 6-1(vì\,\,\sqrt 6-1>0)$
Vậy $\sqrt{7-2\sqrt 6}=\sqrt 6-1$
