点A(cosα,sinα)和点B(1,1)则AB向量的模的最小值是?
问题描述：
点A(cosα,sinα)和点B(1,1)则AB向量的模的最小值是?
答
AB =OB-OA = (1-cosα,1-sinα)
|AB|^2
=(1-cosα)^2+(1-sinα)^2
=2-2(sinα+cosα)
=2- 2√2(sin(α+π/4))
min|AB|=0 at sin(α+π/4) =1/√2