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duong thang d cach deu A,B thi d thuoc mat phang trung truc cua AB.Do d thoc (P) \( \rightarrow d\in (P)\bigcap (Q) \) Goi trung diem I\(\left ( 3/2,5/2,1 \right ) \)cua AB;\(\overrightarrow{BA}\left ( 3,1,0 \right )\Rightarrow \)mat phang trung truc cua AB la:\( \left ( Q\right ):3x+y-7=0 \) co VTPT \( \overrightarrow{n}(3,1,0)\) (P) co VTPT \( \overrightarrow{u}(1,1,1)\) \(\Rightarrow \overrightarrow{d}=\left[ {\overrightarrow{n}\times \overrightarrow{u}} \right]\Rightarrow \)ta viet dc duong thang d co VTCP la\( \overrightarrow{d}\)va di qua diem H(2,1,4) la diem chung cua 2 mat phang (Q) va(P)
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