\[\boxed{\mathbf{Страница\ 41.}еуроки - ответы\ на\ пятёрку}\]
\[\boxed{\mathbf{137.}}\]
\[a = 0:\]
\[85 \cdot a < 85 + a\]
\[a = 6:\]
\[85 \cdot 6 > 85 + 6\]
\[a = 10:\]
\[85 \cdot 10 > 85 + 10\]
\[\boxed{\mathbf{138.}}\]
\[Образуют\ прямой\ угол:\]
\[1)\ \text{AM\ }и\ MK;\]
\[\text{MK\ }и\ KO;\]
\[\text{KO\ }и\ OA;\]
\[\text{OA\ }и\ \text{AM.}\]
\[2)\ AB\ и\ BC;\]
\[\text{BC\ }и\ CM;\]
\[\text{CM\ }и\ MA;\]
\[\text{MA\ }и\ \text{AB.}\]
\[\boxed{\mathbf{139.}}\]