tích vô hướng của 2 vecto

H

hien_vuthithanh

1/ $\vec{HC}$=$\vec{BC}$-$\vec{BH}$ \Rightarrow $HC^2$=$BC^2+BH^2$-2$\vec{BH}$.$\vec{BC}$
\Leftrightarrow $\vec{BH}$.$\vec{BC}$ =$\dfrac{5^2}{2}$=$\dfrac{25}{2}$ (vì BH=HC)
 
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