解析:∵\s\up6(→(→)=\s\up6(→(→)-\s\up6(→(→)=\s\up6(→(→)-\s\up6(→(→),
又\s\up6(→(→)=x\s\up6(→(→)+y\s\up6(→(→)+ \s\up6(→(→),
∴x=,y=0, =-1,即(x,y, )=(,0,-1).
答案:(,0,-1)
设OABC是四面体,G1是△ABC的重心,G是OG1上一点,且OG=3GG1,若\s\up6(→(→)=x\s\up6(→(→)+y\s\up6(→(→)+ \s\up6(→(→),则(x,y, )为 .
解析:\s\up6(→(→)=\s\up6(→(→)-\s\up6(→(→),\s\up6(→(→)=\s\up6(→(→)-\s\up6(→(→),∵G1是△ABC的重心,∴\s\up6(→(→)=(\s\up6(→(→)+\s\up6(→(→))=(\s\up6(→(→)+\s\up6(→(→)-2\s\up6(→(→)),由于OG=3GG1,∴\s\up6(→(→)=\s\up6(→(→)=(\s\up6(→(→)+\s\up6(→(→)-2\s\up6(→(→)),又\s\up6(→(→)=x\s\up6(→(→)+y\s\up6(→(→)+ \s\up6(→(→),
∴(x,y, )=(,,-).
答案:(,,-)
如图,已知正方体ABCDA′B′C′D′,点E是上底面A′B′C′D′的中心,分别取向量\s\up6(→(→),\s\up6(→(→),\s\up6(→(→)为基底,若
(1)\s\up6(→(→)=x\s\up6(→(→)+y\s\up6(→(→)+ \s\up6(→(→);
(2)\s\up6(→(→)=x\s\up6(→(→)+y\s\up6(→(→)+ \s\up6(→(→),试确定x,y, 的值.
解:(1)∵\s\up6(→(→)=\s\up6(→(→)+\s\up6(→(→)=\s\up6(→(→)+\s\up6(→(→)+\s\up6(→(→)=-\s\up6(→(→)+\s\up6(→(→)+\s\up6(→(→),又\s\up6(→(→)=x\s\up6(→(→)+y\s\up6(→(→)+ \s\up6(→(→),∴x=1,y=-1, =1.
(2)∵\s\up6(→(→)=\s\up6(→(→)+\s\up6(→(→)=\s\up6(→(→)+\s\up6(→(→)
=\s\up6(→(→)+(\s\up6(→(→)+\s\up6(→(→))
=\s\up6(→(→)+\s\up6(→(→)+\s\up6(→(→)=\s\up6(→(→)+\s\up6(→(→)+\s\up6(→(→),
又\s\up6(→(→)=x\s\up6(→(→)+y\s\up6(→(→)+ \s\up6(→(→),
∴x=,y=, =1.