Quay lại đáp án

	2	bớt 139 ký tự trong đáp án		Sửa 19-12-13 08:46 AM tieutulitipro 1
$2\overrightarrow{AB}.\overrightarrow{AC} = \overrightarrow{AB}^{2} + \overrightarrow{AC}^{2} - ( \overrightarrow{AB} - \overrightarrow{AC} )^{2} = AB^2 + AC^2 -BC^2 = 40 \Rightarrow \overrightarrow{AB}.\overrightarrow{AC}=20.$ $2\overrightarrow{AB}.\overrightarrow{AC} = \overrightarrow{AB}^{2} + \overrightarrow{AC}^{2} - ( \overrightarrow{AB} - \overrightarrow{AC} )^{2} = AB^2 + AC^2 -BC^2 = 40 \Rightarrow \overrightarrow{AB}.\overrightarrow{AC}=20. theo mình thì k phải là \overrightarrow{AB}.\overrightarrow{AC} =20 mà là cos\overrightarrow{AB}.\overrightarrow{AC}=20 $ $2\overrightarrow{AB}.\overrightarrow{AC} = \overrightarrow{AB}^{2} + \overrightarrow{AC}^{2} - ( \overrightarrow{AB} - \overrightarrow{AC} )^{2} = AB^2 + AC^2 -BC^2 = 40 \Rightarrow \overrightarrow{AB}.\overrightarrow{AC}=20.$

	1	tạo mới		Trả lời 19-12-13 08:42 AM tieutulitipro 1
$2\overrightarrow{AB}.\overrightarrow{AC} = \overrightarrow{AB}^{2} + \overrightarrow{AC}^{2} - ( \overrightarrow{AB} - \overrightarrow{AC} )^{2} = AB^2 + AC^2 -BC^2 = 40 \Rightarrow \overrightarrow{AB}.\overrightarrow{AC}=20. theo mình thì k phải là \overrightarrow{AB}.\overrightarrow{AC} =20 mà là cos\overrightarrow{AB}.\overrightarrow{AC}=20 $

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