§ Задание 54
\[\boxed{\mathbf{6.54}}\]

\[\textbf{а)}\ AB\bot BC;\]
\[\textbf{б)}\frac{\text{AC}}{\text{MN}} = \frac{\text{BC}}{\text{KN}} = \frac{\text{AB}}{\text{MK}}\]
\[\boxed{\mathbf{6.54}}\]

\[\textbf{а)}\ AB\bot BC;\]
\[\textbf{б)}\frac{\text{AC}}{\text{MN}} = \frac{\text{BC}}{\text{KN}} = \frac{\text{AB}}{\text{MK}}\]