Giúp em đc ko mn:((((((

Đáp án+Giải thích các bước giải:

$A=\sqrt{7-2\sqrt{10}}+\sqrt{2}\\ =\sqrt{5-2\sqrt{5}.\sqrt{2}+2}+\sqrt{2}\\ =\sqrt{(\sqrt{5}-\sqrt{2})^2}+\sqrt{2}\\ =|\sqrt{5}-\sqrt{2}|+\sqrt{2}\\ =\sqrt{5}-\sqrt{2}+\sqrt{2}\\ =\sqrt{5}\\ B=\sqrt{13-2\sqrt{42}}\\ =\sqrt{13-2\sqrt{7}.\sqrt{6}}\\ =\sqrt{7-2\sqrt{7}.\sqrt{6}+6}\\ =\sqrt{(\sqrt{7}-\sqrt{6})^2}\\ =|\sqrt{7}-\sqrt{6}|\\ =\sqrt{7}-\sqrt{6}\\ C=\sqrt{46+6\sqrt{5}}\\ =\sqrt{45+2.3\sqrt{5}.1+1}\\ =\sqrt{(3\sqrt{5}+1)^2}\\ =|3\sqrt{5}+1|\\ =3\sqrt{5}+1\\ D=\sqrt{12+3\sqrt{15}}\\ =\dfrac{\sqrt{2}\sqrt{12+3\sqrt{15}}}{\sqrt{2}}\\ =\dfrac{\sqrt{24+2.3\sqrt{15}}}{\sqrt{2}}\\ =\dfrac{\sqrt{15+2.3.\sqrt{15}+9}}{\sqrt{2}}\\ =\dfrac{\sqrt{(3+\sqrt{15})^2}}{\sqrt{2}}\\ =\dfrac{3+\sqrt{15}}{\sqrt{2}}\\ =\dfrac{3\sqrt{2}+\sqrt{30}}{2}\\ E=\sqrt{4-\sqrt{7}}+\sqrt{4+\sqrt{7}}\\ =\dfrac{\sqrt{2}(\sqrt{4-\sqrt{7}}+\sqrt{4+\sqrt{7}})}{\sqrt{2}}\\ =\dfrac{\sqrt{8-2\sqrt{7}}+\sqrt{8+2\sqrt{7}}}{\sqrt{2}}\\ =\dfrac{\sqrt{7-2\sqrt{7}+1}+\sqrt{7+2\sqrt{7}+1}}{\sqrt{2}}\\ =\dfrac{\sqrt{(\sqrt{7}-1)^2}+\sqrt{(\sqrt{7}+1)^2}}{\sqrt{2}}\\ =\dfrac{|\sqrt{7}-1|+|\sqrt{7}+1|}{\sqrt{2}}\\ =\dfrac{\sqrt{7}-1+\sqrt{7}+1}{\sqrt{2}}\\ =\dfrac{2\sqrt{7}}{\sqrt{2}}\\ =\sqrt{2}.\sqrt{7}\\ =\sqrt{14}.$