楼上的不对的,向量夹角的范围:[0,π]π/2+角∈(π,3π/2),是不对的-------------------------------------------------令:角=ta=(2cost,2sint),b=(0,-1)则:a·b=(2cost,2sint)·(0,-1)=-2sint则:cos=a·b/(|a|*|b|)=-2sint/2=-sint=cos(π/2+t)=cos(-π/2-t)=cos(2π-π/2-t)=cos(3π/2-t)t∈(π/2,π),即:-t∈(-π,-π/2)故:3π/2-t∈(π/2,π)故:=3π/2-t...
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