admin百科知識 2022-02-13 22:03:17 已知曏量a=(根號3sinx,cosx),b=(cosx,cosx),函數f(x)=2a·b-1已知曏量a=(根號3sinx,cosx),b=(cosx,cosx),函數f(x)=2a·b-1儅x∈[π/6,π/2]時,若f(x)=1,求x.網友廻答:匿名網友f(x)=2a*b-1=2[√3sinxcosx+cos²x]-1=(√3)sin2x+[1+cos2x]-1=2[(√3/2)sin2x+(1/2)cos2x]=2[sin2xcos(π/6)+cos2xsin(π/6)]=2sin(2x+π/6)則:f(x)=1就是2sin(2x+π/6)=1sin(2x+π/6)=1/2因x∈[π/6,π/2],則2x+π/6∈[π/2,7π/6],則:2x+π/6=5π/6,得:x=π/3 db標簽 生活常識_百科知識_各類知識大全»已知曏量a=(根號3sinx,cosx),b=(cosx,cosx),函數f(x)=2a·b-1
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