`\sqrt{(\sqrt{7} - \sqrt{2})^2} + \sqrt{(\sqrt{7} + \sqrt{2})^2} - \sqrt{28}`

`= |\sqrt{7} - \sqrt{2}| + |\sqrt{7} + \sqrt{2}| - \sqrt{4} . \sqrt{7}`

`= \sqrt{7} - \sqrt{2} + \sqrt{7} + \sqrt{2} - 2\sqrt{7}`

`=(\sqrt{7}+ \sqrt{7}- 2\sqrt{7})+(- \sqrt{2}+ \sqrt{2})`

`=0`