Cho tam.giác ABC , gọi I là điểm trên cạnh BC sao cho 2CI 3BI , gọi J là điểm trên BC kéo dài sao cho 5JB =2JC   a) Tính vectơ AI,AJ theo vectơ AB,AC. b) gọi G là trọng tâm tam giác ABC , Tính vectơ AG theo vectơ AI,AJ
Cảm ơn nhá
Ta có $I\in BC$ và 2 IC= 3BI
$\Rightarrow 2\overrightarrow{IC}= -3\overrightarrow{IB}$
$\Leftrightarrow 3\overrightarrow{IB} + 2\overrightarrow{IC} = 0$
$\Rightarrow 3\overrightarrow{AB}+ 2\overrightarrow{AC} = 5\overrightarrow{AI}$
$\Leftrightarrow \overrightarrow{AI}=\frac{3}{5}\overrightarrow{AB}+\frac{2}{5}\overrightarrow{AC}$
Có 5JB= 2JC $\overrightarrow{JB}= \frac{2}{5}\overrightarrow{JC}$ 
$\Leftrightarrow 5\overrightarrow{JB} - 2\overrightarrow{JC} = 0 $
$\Rightarrow 5\overrightarrow{AB} -2\overrightarrow{AC} = 3\overrightarrow{AI}$
$\Leftrightarrow\overrightarrow{AJ} = \frac{5}{3}\overrightarrow{AB} -\frac{2}{3}\overrightarrow{AC}$
 Mk đang bận nên lm z thui nhé


trình bày đập vào mặt ng xem,ko giật mk hơi lạ –  Ngọc 06-07-16 08:26 AM
S giật mk a,lm bài cn trình bày ác liệt hơn –  Kaito kid 06-07-16 08:23 AM
trình bày sống động quá làm e giật cả mk :| –  Ngọc 06-07-16 08:18 AM

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