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let Q be k(1,1,2)QA.QB= (OA-OQ).(OB-OQ)= (1-k,2-k,3-2k).(2-k,1-k,2-2k)=(1-k)(2-k)+(2-k)(1-k)+(3-2k)(2-2k)=(1-k)(4-2k+6-4k)=2(1-k)(5-3k)(QA.QB)' = 2[-3(1-k) -(5-3k)]=0-3+3k-5+3k=0 6k=8k =4/3(min)min QA.OB= 2(1-4/3)(5-3(4/3)) = 2(-1/3)= -2/3 Q = (4/3)(1,1,2)... |
