\[\boxed{\mathbf{1229\ (1229)}\mathbf{.}\mathbf{\ }Еуроки\ - \ ДЗ\ без\ мороки}\]
\[1)\ AB\bot AD\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \]
\[\ \ \ 2)\ AB\bot AD;\ \ AB\bot BC\ \ \ \ \ \ \ \ \]
\[\ \ \ \ \ 3)\ AB\bot AD;\ \ BC\bot CD\]