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ǰλãҳ >> Ϊʲôsin2x=2sinxCosx >>

Ϊʲôsin2x=2sinxCosx

Ǻ͵ҹʽ sin(x+x) = sinx cosx + cosx sinx = 2 sinx cosx

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sin(x+x)=sinx*cosx+cosx*sinx=2sinx*cosx Ǻ͵ʽ

¥ sinAcosA+cosAsinA = sinAcosA+sinAcosA Ȼ󲻾2sinAcosA

sin(+)=sincos+cossin£ sin2x =sin(x+x) =sinxcosx+cosxsinx =2sinxcosx

sin(x+x)=sinxcosx+cosxsinx=2sinxcosx cos(x+x)=cosxcosx-sinxsinx=(cosx)^2-(sinx)^2 ֱӺͼ1=(sinx)^2+(cosx)^2 sin2x=2sinxcossin(a+b)=sinacosb+cosasinbƳ cos2x=1-(2sinx)^2 or (2cosx)^2-1,ͬ cos(a+b)=cosacosb-...

sin2x=2sinxcosx (sin2x)/2=sinxcosx ֻcosx=1ʱsin2xŵsinx

ԴӺͽǹʽôƵ sin2x=sin(x+x) =sinxcosx+cosxsinx =2sinxcosx

Ϊ sin(x+y)=sin(x)cos(y)+cos(x)sin(y) sin(2x)=sin(x+x)=sin(x)cos(x)+cos(x)sin(x)=2sin(x)cos(x).

lim[(sin2x)/x]=lim[(2sinxcosx)/x]=lim{[(2sinx)/x]•cosx}

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