f(x)=a*b-4mcosx+2|b|^2
=cos(3x/2)cos(x/2)-sin(3x/2)sin(x/2)-4mcosx+2
=cos(3x/2+x/2)-4mcosx+2
=cos(2x)-4mcosx+2
=2(cosx)^2-1-4mcosx+2
=2(cosx-m)^2+1-2m^2 .
因为 x∈[-π/2,0] ,因此 0
已知向量a=(cos(3x/2),sin(3x/2)),向量b=(cos(x/2),-sin(x/2)),其中x∈[-π
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