[Toán 10]Tích vô hướng !

E

e.l.f

[TEX]4\vec{MH}.\vec{MA}=4\vec{HM}.\vec{AM}[/TEX]
[TEX]\Rightarrow 4\vec{HM}.\vec{AM}=(\vec{HB}+\vec{HC})(\vec{AB}+\vec{AC})[/TEX][TEX]=(\vec{HK}+\vec{KB}+\vec{KC}-\vec{HK})(\vec{AK}+\vec{KB}+\vec{KC}-\vec{AK})[/TEX][TEX](\vec{KB}+\vec{KC})^2[/TEX][TEX]=BC^2[/TEX]Trong đó K là giao điểm của AB vs CH​
 
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