Giúp em với ạ em cảm ơn trước nha Rút gọn: a) √8-2 √7 b) √7-2√10 + √2

a) $\sqrt[]{8-2\sqrt[]{7}}$

$=\sqrt[]{(\sqrt[]{7})^2-2.\sqrt[]{7}.1+1}$

$=\sqrt[]{(\sqrt[]{7}-1)^2}$

$=|\sqrt[]{7}-1|$

$=\sqrt[]{7}-1$

b) $\sqrt[]{7-2\sqrt[]{10}}+\sqrt[]{2}$

$=\sqrt[]{(\sqrt[]{5})^2-2.\sqrt[]{5}.\sqrt[]{2}+(\sqrt[]{2})^2}+\sqrt[]{2}$

$=\sqrt[]{(\sqrt[]{5}-\sqrt[]{2})^2}+\sqrt[]{2}$

$=|\sqrt[]{5}-\sqrt[]{2}|+\sqrt[]{2}$

$=\sqrt[]{5}-\sqrt[]{2}+\sqrt[]{2}$

$=\sqrt[]{5}$