Đáp án:
\(\eqalign{
& b)\,\,M\,\,la\,\,dinh\,\,thu\,\,tu\,\,cua\,\,hinh\,\,binh\,\,hanh\,\,ABCM. \cr
& c)\,\,Tap\,\,hop\,\,diem\,\,M\,\,la\,\,duong\,\,tron\,\,tam\,\,I,\,\,ban\,\,kinh\,\,{1 \over 2}AB\,\, - \,\,I\,\,la\,\,TD\,\,AB. \cr} \)
Giải thích các bước giải:
\(\eqalign{
& b)\,\,\overrightarrow {MA} - \overrightarrow {MB} + \overrightarrow {MC} = \overrightarrow 0 \cr
& \Leftrightarrow \overrightarrow {MA} - \overrightarrow {MA} - \overrightarrow {AB} + \overrightarrow {MA} + \overrightarrow {AC} = \overrightarrow 0 \cr
& \Leftrightarrow \overrightarrow {MA} = \overrightarrow {AB} - \overrightarrow {AC} \cr
& \Leftrightarrow \overrightarrow {MA} = \overrightarrow {CB} \cr
& \Rightarrow M\,\,la\,\,dinh\,\,thu\,\,tu\,\,cua\,\,hinh\,\,binh\,\,hanh\,\,ABCM. \cr
& c)\,\,\left| {\overrightarrow {MA} + \overrightarrow {MB} } \right| = \left| {\overrightarrow {MA} - \overrightarrow {MB} } \right| \cr
& \Leftrightarrow \left| {2\overrightarrow {MI} } \right| = \left| {\overrightarrow {MA} - \overrightarrow {MA} - \overrightarrow {AB} } \right| \cr
& \Leftrightarrow 2MI = AB\,\,\left( {I\,\,la\,\,TD\,cua\,AB} \right) \cr
& \Rightarrow MI = {1 \over 2}AB \cr
& \Rightarrow Tap\,\,hop\,\,diem\,\,M\,\,la\,\,duong\,\,tron\,\,tam\,\,I,\,\,ban\,\,kinh\,\,{1 \over 2}AB \cr} \)
