Ta có: \(A=\dfrac{\sqrt{28}}{\sqrt{7}}+\dfrac{\sqrt{50}-\sqrt{10}}{\sqrt{2}}+\sqrt{2}\cdot\sqrt{10}\)
\(=\sqrt{\dfrac{28}{7}}+\dfrac{\sqrt{50}}{\sqrt{2}}-\dfrac{\sqrt{10}}{2}+\sqrt{2\cdot10}\)
\(=\sqrt{\dfrac{28}{7}}+\sqrt{25}-\sqrt{5}+\sqrt{20}\)
\(=2+5-\sqrt{5}+2\sqrt{5}=7+\sqrt{5}\)