Question

căn 4 - căn 7 + căn 4 + căn 7

Answer 1

\(\sqrt{4}-\sqrt{7}+\sqrt{4}+\sqrt{7}\\ =\left(\sqrt{4}+\sqrt{4}\right)+\left(-\sqrt{7}+\sqrt{7}\right)\\ =2+2+0\\ =4\)

Answer 2

=\(\dfrac{1}{\sqrt{2}}\left(\sqrt{8-2\sqrt{7}}+\sqrt{8+2\sqrt{7}}\right)\)

\(=\dfrac{1}{\sqrt{2}}\left(\sqrt{7}-1+\sqrt{7}+1\right)=\dfrac{2\sqrt{7}}{\sqrt{2}}=\sqrt{14}\)