\(\sqrt{4+\sqrt{7}}-\sqrt{4-\sqrt{7}}-\sqrt{2}\)
\(=\sqrt{\dfrac{2\left(4+\sqrt{7}\right)}{2}}-\sqrt{\dfrac{2\left(4-2\sqrt{7}\right)}{2}}-\sqrt{2}\)
\(=\sqrt{\dfrac{8+2\sqrt{7}}{2}}-\sqrt{\dfrac{8-2\sqrt{7}}{2}}-\sqrt{2}\)
\(=\sqrt{\dfrac{\left(\sqrt{7}\right)^2+2\sqrt{7}+1}{2}}-\sqrt{\dfrac{\left(\sqrt{7}\right)^2-2\sqrt{7}+1}{2}}-\sqrt{2}\)
\(=\sqrt{\dfrac{\left(\sqrt{7}+1\right)^2}{2}}-\sqrt{\dfrac{\left(\sqrt{7}-1\right)^2}{2}}-\sqrt{2}\)
\(=\dfrac{|\sqrt{7}+1|}{\sqrt{2}}-\dfrac{|\sqrt{7}-1|}{\sqrt{2}}-\sqrt{2}\)
\(=\dfrac{\sqrt{7}+1}{\sqrt{2}}-\dfrac{\sqrt{7}-1}{\sqrt{2}}-\dfrac{2}{\sqrt{2}}\)
\(=\dfrac{0}{\sqrt{2}}=0\)
\(\sqrt{4}+\sqrt{\sqrt{7}}-\sqrt{4}-\sqrt{\sqrt{7}}-\sqrt{2}\) \(=-\sqrt{2}\)
mik chk hk lp 9, nhưng mik nhớ bữa lp 7 nên làm vậy
em cảm mơn nhìu nhìu 
