|OA|=|OB|,说明O点在AB的平分线上,当C是AB的中点时,|OC|取最小值
此时OA与OC的夹角为π/3,OB与OC的夹角为π/3,即OA与OB的夹角为2π/3
|OA-tOB|^2=(OA-tOB)·(OA-tOB)=|OA|^2+t^2|OB|^2-2tOAOB
=4+4t^2-2t*4*cos(2π/3)=4t^2+4+4t=4(t+1/2)^2+3,故:|OA-tOB|^2的最小值是3
即|OA-tOB|的最小值是sqrt(3)
|OA|=|OB|,说明O点在AB的平分线上,当C是AB的中点时,|OC|取最小值
此时OA与OC的夹角为π/3,OB与OC的夹角为π/3,即OA与OB的夹角为2π/3
|OA-tOB|^2=(OA-tOB)·(OA-tOB)=|OA|^2+t^2|OB|^2-2tOAOB
=4+4t^2-2t*4*cos(2π/3)=4t^2+4+4t=4(t+1/2)^2+3,故:|OA-tOB|^2的最小值是3
即|OA-tOB|的最小值是sqrt(3)