hinhhocl0p11

A

aquylani_1912

goi Ot,Ov,Op lan luot la pg cac goc xOy,yOz, zOx.
A,B,C lan luot lathuoc Ox, Oy, oz sao cho Ot,Ov la trung truc cua AB,BC
M=AB giaoOt, N=BC giaoOv
MN//AC suy ra MN//(OAC)nen MN//op
vay OM,ON,Op dong phang suyra dpcm.
 
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