Giải các bài toán vector

S

starteen97

N

nttthn_97

$M\in(d)$[TEX]\Rightarrow[/TEX]$M(2a-1;a)$
$2\vec{MA}=(4-4a;6-2a)$
$\vec{MB}=(-4-2a;-3-a)$
$2\vec{MA}+\vec{MB}=(-6a;3-3a)$
[TEX]|2\vec{MA}+\vec{MB}|[/TEX]=$\sqrt{36a^2+9a^2-18a+9}$= $\sqrt{45(a-\frac{1}{5})^2+\frac{36}{5}}$[TEX]\geq[/TEX] $\frac{6}{\sqrt{5}}$
$|2\vec{MA}+\vec{MB}| min=\frac{6}{\sqrt{5}}$[TEX]\Leftrightarrow[/TEX]$a=\frac{1}{5}$[TEX]\Rightarrow[/TEX]$M(\frac{-3}{5};\frac{1}{5})$
 
Last edited by a moderator:
You must log in or register to reply here.
Top Bottom