The side of square is \\\\(10\\ cm\\\\)In right angled \\\\(\ riangle ABD\\\\)\\\\(AB^{2} + AD^{2} = BD^{2}\\\\) [according to Pythagoras theorem]\\\\((10)^{2} + (10)^{2} = BD^{2}\\\\) \\\\(100 + 100 = BD^{2}\\\\)\\\\(BD^{2} = 200\\\\)\\\\(BD = 10\\sqrt {2}cm\\\\)\\\\(\ herefore\\\\) Diagonal of square \\\\(= 10 \\sqrt {2}cm\\\\).