Đáp án:
d) \(\overrightarrow {AM} = \frac{1}{2}\overrightarrow {AB} + \overrightarrow {AD}\)
Giải thích các bước giải:
$\begin{array}{l}
Cau\,2:\\
c)Ta\,co:\\
\overrightarrow {AB} + \overrightarrow {IA} = \overrightarrow {IA} + \overrightarrow {AB} = \overrightarrow {IB} \left( {dpcm} \right)\\
d)Vi\,M\,la\,trung\,diem\,CD\,nen:\\
\overrightarrow {AM} = \frac{1}{2}\left( {\overrightarrow {AC} + \overrightarrow {AD} } \right)\\
Ma\,ABCD\,la\,hinh\,binh\,hanh\,nen\,\overrightarrow {AC} = \overrightarrow {AB} + \overrightarrow {AD} \\
\Rightarrow \overrightarrow {AM} = \frac{1}{2}\left( {\overrightarrow {AC} + \overrightarrow {AD} } \right) = \frac{1}{2}\left( {\overrightarrow {AB} + \overrightarrow {AD} + \overrightarrow {AD} } \right)\\
= \frac{1}{2}\left( {\overrightarrow {AB} + 2\overrightarrow {AD} } \right) = \frac{1}{2}\overrightarrow {AB} + \overrightarrow {AD} \\
Vay\,\overrightarrow {AM} = \frac{1}{2}\overrightarrow {AB} + \overrightarrow {AD}
\end{array}$
