2 .15 .BD :√2 BD = √2 .16 2 2 = √2 2 AC /∙ 2 4 2 = √2 AC /: √2 √= 2 -1. - 1 +1 .17 =( )(-2 -1 2 −1 2 )( ) .( < <) 21 = −1 . 2 5